help! need advice about in laws

so my In law loves to take our two daughters every other weekend to her house. my youngest is in diapers. here lately I've noticed she comes home with no diapers and has a rash. I always pack the diaper bag full. it's only a day and half that she is there and she always goes through all the diapers. I've also noticed that her husband granddaughter is always there when my children are. Their parents are mooches and beg for diaper and formula money all the time from my husbands parents. They are drugs addicts, stole his moms jewelry and pawned it etc. so at this point I'm pretty sure they are using my childs diapers on this other child. leaving my daughter with a rash. I am beyond livid. my husband refuses to say anything to his mother and I do not want to send my child back over if this is going to keep happening. that child is not my responsibility and my child shouldn't be suffering because of it. the parents have money they have jobs. they'd rather spend it on motorcycles and drugs. while his step dad enables it by giving them money all the time. am I wrong for being mad. I want to say something but his family is notorious for calling me a bitch if I ever say anything negative and I always look like the bad guy. also I have been sending a training potty with my child.