Please some advice

My son is 8 years old and has ADHD and conduct disorder. He is always stealing stuff(only in my house). He literally will take stuff like soda pop, candy, video games, his sister’s toys, etc. we have told him just to ask and we will get him it, but still at night he is taking things or durning the time I’m taking care of his baby sister by myself(meaning my husband is at work). I don’t know how to stop him from doing it. We ask him why he does it and he just says he can’t remember why. I have asked his dad if he does it there and they say no, because their stuff is locked up because they share a house with others so they lock their room when they aren’t in it, so he can’t do it even if he wanted too. Anyone else have this problem? He gets everything when he ask, we don’t say no much unless he already had that thing he is asking for or to much sweets that day, or he needs to read/play outside and not play video games on school nights..