I totally understand your concern and will agree with you the situation does seem very strange. Honestly I’m still trying to understand why he would want to wear diapers at all. But obviously this is a thing.
To answer a few questions, yes he is on the spectrum, however he is high functioning. Being autistic has played a big part of his potty training troubles, that and bedwetting being hereditary. We have had him try to diaper himself but he does a horrible job at it. Never gets the tapes right and it ends up being so loose it leaks horribly I know he could do better if he really tried but I don’t think he wants to. Should I make him? Tell him if he wants to wear diapers it’s all on his own and we won’t be helping? Or do we support him in his wanting to wear diapers? This is a genuine question. As for his sister helping it’s only if I’m not available, and she has has been helping him since he was little so I guess it just kept on. I also have a 4 year old who is finally potty trained, wears underwear during the day, with 2 exceptions, he still wets the bed and refuses to poop in anything but a diaper. She still helps him if I’m busy and honestly Jacob will go to her for a change if needed and she is already changing my little guy. Jacob my older son hasn’t started puberty so maybe that is why he still isn’t modest at all?
I hope this answers some of your questions.