Just so you know, we took this feedback very seriously and already developing Chocolate Milf, Milf with cuck husband, Aunt and her daughter and GILF.
Here is example of aunt and niece character sheets and draft art:
Aunt and cousin. Aunt has many traits of classic bimbo. She's about 35 y. o. but looks and acts like 25, with low waist jeans and crop top that squashes her breast into one monolith boob. She's not a bad person but can be a bit obnoxious with her "independent woman" act. She's not talked about in the family because of her career choice (either stripper or a porn actress, to be decided). In second option MC can be watching some milf porn (because he's horny for his mom and all) and find a video with his aunt. As for the cousin, we imagine her being a "quirky girl" type. Her mom lets her do whatever, so she's a bit of a brat and acts more mature than she actually is, and she's dressed like a little whore.
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Given that you want to listen I'll write a little more about gamedev and then I'll respond to your future changes as well:
I'm glad you're motivated and ambitious in regards to your game, I already mentioned the importance of consistency but I want to reiterate. I hope you're going to care about making something worthwhile as a gaming experience in general, even in the case later on of your game being a big success I hope you won't start drip feeding content for easy monthly patreon money like most (basically every top earner) dev.
But there is also the other side as well, with even more devs on it. The side where devs pour their hearts into the game and after a few months when they don't see a 1 to 1 return on their passion in terms of the community response they lose all hope and stop developing the game altogether, as is the main reason for so many [Abandoned] games on this site.
In the game dev industry one of the important things is to understand the possibility of reality where your first game, usually the most ambitious one, might not be the holy grail of whatever you imagine it being. A lot of times it takes practice and repetiton before you can make something that truly clicks, and with a solid amount of luck also gets popular.
For now my advice is, do your best and focus on developing this as far into the story as you can but, in the case where you, for whatever reason, want to stop working on the game, try to power through finishing it up within a couple of updates so you can have a complete product. And then think about new ideas and use the knowledge you've gained in your next game and do even better.
There aren't many devs with multiple games on here but in almost all the cases, their second and later on games are much better and popular than the ones before.
And in regards to the Aunt and the cousin, they look great, the only thing I feel like definitely needs to happen is the career choice to be camming rather than being a pornstar or stripper given the implied NTR within those options. This is also the usual option devs go for as its the simplest one. The example here being the MCs camwhore aunt in "The Twist".
In that and many other games with incest with the aunt there is also the great dynamic of jealousy between the MCs mother and the aunt as the aunt is flirting and basically wanting the steal the MC from the mother.
It wouldn't be too bad to write that in. The mother knows the aunt is a camwhore and doesn't want her around her son, you can have a lot of flirty moments where the MC meets the aunt, the mom getting jealous about MC hugging and kissing the aunt etc.
A small personal preference I would like to see is also a tanned character with tanlines, I guess the aunt bimbo would be a good choice for that, it also adds free dialogue between the MC and the aunt which can go tanning at the beach and talk about the tan and for the MC to apply sunscreen to her body etc.
The cousin characters seems nice as well, making brats beg is always entertaining.
As the last thing about the popularity of H games. The reality is, unless you were a really early pioneer, from what I see, 90% of the success formula is presentation. In 2D gamedev most of that presentation falls directly onto the artists hands unlike 3D where it's more about working with 3D models, posing and lighting. The good thing about 2D games is, if they are done well they can be much more memorable and unique than your average 3D game regardless of how detailed the models in that games are (for example Aurelia).
So I would recommend you look at some of those more popular 2D games and see also how they "feel" overall when it comes to the gameplay, all of them are obviously simple dialogue/inventory/map clickers but there is a lot of soul you can put in the UI which won't take too long and it's something the player will see in every single scene and will contribute to their experience.
Look through these games and get some ideas about what you could implement in your game that could work in terms of that game feel: What a Legend, My Pig Princess, Taffy Tales, Aurelia, Hero Party Must Fall, Knightly Passions and even Summertime Saga.
You also can look at very simple looking games likes "The Grim Reaper who reaped my Heart" and see what exactly did they do to induce the comfy atmosphere.
But basically, try to play around with vignettes, scene transitions, characters sliding in and out of the scene etc. Whatever you see happening in the games above that might work, especially the first three as they have the most effort put into them although i really advise you play through all of the games in my first post to understand why some with not too much art put into them still managed to succeed (Hero Party Must Fall especially).
Also look through how these games present themselves on f95 with promo material as well, make sure all of the promo material is up to date with new character at all times and all the different characters are presented well as a lot of people at least try out a lot of games for only one character they see and like among a dozen of them. Look through other sites you can upload your game on: itch, other sites similar to f95 and later on when you have a complete game version maybe even Steam, as H games on there also get solid visibility.
Cheers