For the beta/alpha route stuff, logically speaking, MC being beta or alpha shouldn't impact how mom/sis act. They should, in theory, be the same person regardless of how MC acts. Thus, for the sake of consistent personalities, the beta route should develop a lot slower to match the alpha pace, or the other way around.
Now, also logically speaking, mom/sis shouldn't view MC as a LI, he is their family member. So it makes sense for the alpha route to be slower, but not significantly slower, just to keep the routes comparable in terms of content.
It would make sense for the alpha route to be 2 or so updates behind in sexual content, to keep the buildup reasonable, then the alpha route would catch up and at the end the routes have equal content.