Personally i think it's a bad decision to build a game for a vague minority, but hey ... they also have all rights to get a game for THEIR taste too. If the dev is ok with creating a game without that much support (financially), there's nothing wrong with it - just saying.
This, definitely this.
This game reminds me a bit of an AVN called Reparations. It was a passion project for that Dev too. He set out to make a game that was offensive to pretty much everyone and succeeded a bit too well. As long as there is the knowledge that passion project, a lot of times, means self-financed, more power to you.
I personally think that NTR and incest fetishes clash pretty hard, as most fans of incest don't like having their family members stolen, but there may be a small overlap.
If there was a path for the MC to steal the Mum and cuck the BF that would be pretty awesome.
Just my 2 cents as unavoidable NTR is not for me. Either way best of luck Dev.
And kudos for not even trying to pull this off with Patreon, that was a wise choice.