Changing character designs is fine reworking is done a lot in games. I find most of the time they are a improvement, but you do risk losing some people who enjoyed the original.
Slow update is fine if the Dev is still talking about the game and posting time frames giving something I can look forward too. Otherwise I just end up moving on and forgetting about it.
Most of time the story telling is better when mom/sister corrupts the younger one. Trying for younger bother/son that tries to pervert the mother/sister is a harder story to get it right. Most of time it just turns into they were all perverts the whole time.
I don't mind if they are big but when they get "donkey/horse/elephant" size I just can't help but think about how you would pass out from blood loss every time you whipped it out. Now I am think about human anatomy and the mood is gone time for a new game.