How is sacrificing your mother a “small sacrifice?”
You control the story. It doesn’t control you. If the MC will never become strong enough to stand up to his older brother then you have created a MC that will not be enjoyable to many players. Weakness in a story only works if it grows into strength and is over come. But if you want to force such a choice then that’s your prerogative. If my bother was keeping me from saying my mother’s life I would kill him, even IRL, if the choice was my brother endangering my mother or me taking him out, that’s an easy choice. The MC sounds like he’s unwilling to ever stand up to him, so going with brother sounds like the MC will only do what the brother allows him to. So the MC can get with mom because the older brother allows it, making your MC sound weak and pathetic. But maybe I’m reading too much into your words. And if the brother is keeping the MC from being able to save his mother and build a harem then it is hard to trust that the brother isn’t going “do things” behind the scenes. What authority does the older brother have that is so strong that he decided to let the MC be with mother? Why can’t the MC just become strong enough at some point to defeat him? It sounds like the choice is, run away and be afraid of brother forever or stay and be afraid of brother forever and get his cast offs and allowances… where is the growth into a better man who is not forever in his brother’s shadow?
It seems like this game isn’t going to be enjoyable for vanilla fans, or harem or incest fans. There is a disconnect between the promise of no NTR and the existence of an older brother and a story line that is forcing the MC to abandon love interests and remain under his brother’s thumb because the MC is too weak to do anything about it. Or seemingly to escape his brother but leave his mother to an unknown fate.
I’ve been a writer for the better part of 30 years, I was even a writing teacher for several years. And the biggest principle ever storyteller needs to remember is you control the story, not the other way around… only slightly less important is to remember that you should know your audience if you hope to sale the work. I hope you find your audience, and I wish you the best. But it seems you would like to attract incest, harem, and vanilla fans but your story is set up going in a different direction… best of luck.