I believe i can answer these.
1. the school uniforms are custom made for each student and the students get more as they grow, it's talked about in the game. So the uniforms are not actually stretching or growing along with the students. There is no such thing as necessary nudity either, with enough fabric any growth can be clothed.
2. it's a kink game and the physics do not have to match reality especially since these girls factors are also stated to help their bodies support their growths. Ie. honoka gets a strong ass back so she can carry her hooters. I have been a pregnancy fan for years and i have never seen a real pregnancy where a women has become immobile due to her weight, so Aida along with her factor boosted legs and back should be able to stand and walk around or waddle around more accurately.
3. Not true, If you don't take Aidas route she is just your friend and not family. She only becomes your family if you choose her route and impregnate her. otherwise she is impregnated by somone else and you just remain her friend.
4. No, the devs have made it clear this is a romance story between the Main Character and your choice of one of the girls. It is more a romance story than it is a porn game to some degree, Tons of effort goes into the story and writing and characters to show how their relationship blooms and there are only a few actual adult scenes in the game especially compared to the rest of the content. Harem is not the route they wish to take with the title especially considering all the rewriting and new coding it would require.
Hope I answered all your questions.