I understand your points. And while I agree a lot with them, I do understand MC's position, if only in perspective.
He is written as a father first and a lover second, which is not how these game usually go, where daddy is really just a lover with the kink of being the father to make it a slightly forbidden. This last aspect is even worse in harem family setting, which are really just crap. After all, if everybody agrees and everybody is happy about it, is incest really hot?
But I digress. The whole point is that MC is prioritizing his position as father. So, while he is there in a position we all would love to be, he is having the whole "is this the best for my daughters?" kind of conflicting positions in his head. Becca kind of pointed this out when she try to push him to be the one guy Lilith needs, that will love her and never abandon her.
But overall, yes, while I can understand MC's contradicting ways, it is starting to become time when he makes up his mind. His daughters are happy, he is happy, their love is truly eternal.. he has clearly not been a predator trying to push this on his daughters... I would stop doubting and simply be happy. Which also means that the story should be over soon. After all, no conflict, no story to tell.