So from what i see in the thread because Through spacetime was a financial disaster the dev is doing a fuck you harem fans in this game you will not have harem. Maybe i do a route if you splash the money
Jokes aside Through spacetime had a weak story and little emotional attachment basically ' oh look i have big dick, wanna fuck'. It was destined to only be a fap game and an average one at that so it's failure isn't surprising. There are Harem games with good stories where you can see the emotional connection between both mc and the Lis themselves and how the multiple relationships works out. Personally i think it's easier to make a realistic harem between family members than between strangers.
That being said you as the dev think you're not gonna be able to do a good story if the house becomes an full on orgy then its better than butchering the story as per fans' demand which makes it easier for dev to lose interest in game then it gets abandoned. What you are planning with a semi-harem is also good.
As long as i get my throuple with Lilith and one of the sister, no need to throw you in a burning house with the only choice being a slow death or... an even slower death