Thanks for the well reasoned and sober response. You make a lot of good points. This is the type of criticism I like to read here, rather than just "NTR, ..., the LIs are dead to me, curse the devs, etc, etc."
I'll address a few of your points, but I think the main difference between you and myself, is I've never taken Sunshine Love seriously. The writing has always been pretty terrible, and none of the story ever made much logical sense. This is not "Leap of Faith" or "One Day at a Time" both with excellent writing and a detailed, logically thought out and rewarding story. Mr. Dots games, have always been pretty much fluff, in my book. Melody was a bit of an anomoly and really the high point in character development and writing for his team, though it got somewhat repetitive and boring after about the 2/3rds mark. Sunshine Love, to me, has always been like an ice cream Sunday, or perhaps a doughnut; tastes good at the time, but not a lot there to think about.
But, he can't actually, he is forced to stay friendly with them no matter what and act like all is fine and dandy. You can stop having sex and the reason given is laughable, since he says they are close to the villain of the story and their connection with him is dangerous, yet keeps working closely with them in the business that the villain wants to take and he is still friends with them.

The goody two-shoes law graduate has no problem with the fact that they are using brainwashed church girls, or that its illegal, disgusting, or immoral. I mean he never had a backbone the entire game, but cmon
I agree completely with all of this. Instead of the lame rewrite, I would keep the Twins as in the original version, perhaps showing a little more contrition or awareness of their part in the conspiracy, or even own it and be proud of their part to play, and have the MC have the real option to go along with it, or show understandable outrage.
They have more screen time and longer relationship routes than confirmed main LI Ashley, have the same relationship structure as Shortcake(Main LI), Ashley(Main LI), Victoria(Confirmed to get an ending), only Sister is categorically more prominent than the Twins.
That is true regarding the screen time, but the Twins said from the beginning that they weren't interested in a relationship, which I believed, and their actions throughout the game show they they think of the MC as a fun plaything, and not much else. I put them in the same category as Jasmine or Trisha. A fun diversion, but nothing serious or to care about as an MC. Actually, Jasmine cares more about the MC, despite her limited screen time, than the Twins ever did. There is certainly no indication the Twins are interested in the MC as a person, other than for a little fun when they have a free moment. Nothing wrong with that, but than why should the MC care what they do on their own time either.
The most viewed and 3rd best rated game on the site has plenty of prostitute LI and they are major fan favorite characters. Instead of crying about NTR, people are begging the developer, lets call him Pinkman, to upgrade them to main status and get a happy ending. You know why? Because it respects the player's time and investment and gives them information about what type of girls they are BEFORE you have any relation with them, doesn't Rian Johnson your expectations 2 updates before the end of the game for cheap shock value. At that point if someone is going after these type of characters, the dev is in the clear and its 100% on the player.
You will get no argument from me that the game you mention has much better writing and characterization. I have my issues with that game, especially the later updates, but the writing and story has always been top notch. Unlike "Pinkman", Mr. Dots does not have the story well planned out from the beginning, and its obvious. I think their team has a rough outline of what they intend to do, and let Patreon feedback guide their storyline each update, which is why it all seems so disjointed. Look at Yuki? She seemed like a major LI from the beginning, but her character has basically disappeared. I guess the fans didn't like her. That's the problem with too many LIs and no fixed plan. It all seems ad-hoc.
I think the plan was always for the Twins to be Escorts, in the typical meaning, and for it to be a big reveal. There were plenty of clues in the game that they weren't being straight with the MC about many things. The reveal was handled sloppily to be sure. It would have been much better if they didn't pare the big reveal with a sex scene, and had the MC be legitimately shocked and mull over the implications for a few days before deciding to accept or reject the situation with the Twins. That would have been better, more realistic storytelling.
From your posts it seems you have no problem because you enjoy this type of content, I do too, but since I don't play VNs for kinks, I happen to care about the story and characters more, and this right here sacrifices character development in favor of awkwardly setting up a fan service kink later down the line. Its the execution that kills it, not the fact that it happens.
I personally had no problem with the Sis-Vicky scene, which was pretty hot. Sis is the most bland character of the bunch, and Vicky is basically been forgotten after the second update, so a little spice between them was a nice change. Vicky is one of my favorite and sexiest LIs, as a player, but it seems nobody else cares for her, so like Yuki, Mr. Dots has kicked her character to the curb. At lease we get a hot parting scene, both in this update, and the next, I expect.
Yes, the FF attraction was not telegraphed at all, and was obviously shoe-horned in. Probably due to some poll or something. It would have been better to give a few hints of their attraction, at least from Vicky's perspective, over the last 3 or 4 updates, to better build the characterization and make the whole scene fit better in the story, but that is par for the course with Mr. Dots games. Each update is just whatever scenes they feel like having.
Sunshine Love really doesn't have much of a story. The MC leaves his boring life for a women-filled summer at his sister's hotel. That is basically it. There is some filler about the mayor, which nobody cares about, and some sort of sneaky dealings on at a church, but its not like the MC is super religious and a church member, so as a player why do we care? We don't. It all basically meaningless filler for the MC to go on one date or liaison or another with a rotating group of available LIs.
tl, dr, If you would have told me that the game changed writers this update and the new one knows only the synopsis of what has happened in the game so far, I would have no trouble believing you, because there are major continuity problems and it feels like you skipped at least 2 updates worth of content between MC, the Sister and Vicky.
I still can't really understand how its possible that after 7 years, 3 games and past controversies where they allegedly promised to not try to push shady stuff onto their overwelmingly vanilla audience, they couldn't anticipate how this will be received, or think of a better setup for these storylines. Its what made me play for more than a week straight, trying every possible route, because I was fascinated by this drama and how down right shocking it is that it exists. And for once its not the 'purists' fault, its 100% self inflicted.
I agree with the skipped 2 updates part. They should have left a few hints a few updates ago about Vickey's feelings. Sis pretty much just went along with it, since she was drunk, felt left out with the MC going off with other LIs all the time, and just went with it in the moment. No need to read more into it. But Vicky seems to have planned it out, at least a bit, so a little foreshadowing would have went a long way to make it more believable.
You could be right about the writers. But the writing has mostly been pretty poor. It was decent the first few updates, until just after the burlesque scene with Ashley and the MC, when the story sort of made sense. I thought it would be a character driven story about the Sis, her issues with her mom Ashley, and the split with the MCs dad, all with the MC in the middle, and a similar variation of the story with Shortcake and Theresa, but declined since then, with more and more side characters, with the main characters from the beginning being neglected and their stories forgotten or rushed. We still haven't seen any focus at all on what is going on with Sis and Ashley, and how the MC is going to get out of the jam of seeing both of them. That would be actually interesting and fun. Instead we have these pointless stories about some sort of election (always an excitement for AVN players), a priest we don't care about, Sis's ex boyfriend, who keeps popping up, and some unseen church girls. Honestly, who cares about any of it?
Ultimately, the writing on the wall for the decline in story-telling and characterization of Sunshine Love has been there for at least a year. If you expect a fully logical story and deep characterization, you will be dissapointed at every turn. If you just play it like the fluff it is, with better than average renders, and some basic characterization, mostly fun and sexy characters (esp. Ashley, whew), with some fun scenes with a little humor thrown in, with nothing too deep going on, it's easier to just enjoy it.