Trigger warning - Abuse

We just found out that my husbands older sister (my SIL) was sexually abused twice by their dad about 30 years go now. She didn’t go into the details of it and we didn’t ask because I feel that if she wanted us to know that she would have told us and also I’m not sure I want to know as I already feel sick to my stomach. He has admitted to it and apologised. She told us because we have a 12 month old baby girl and would be devastated if anything were to happen to her niece (our girl has never stayed there alone). Now given that was 30 years ago and nothing has happened since (younger sister wasn’t touched either) we don’t know that anything could happen to our baby but then again we don’t know that it wouldn’t so we have decided our baby girl won’t be having sleepovers just to be on the safe side. Her older brother (8 YO) has been having a few days to a week through school holidays ect though since he was 12 months old and he loves it, he loves going there. Our son is Autistic, only slightly verbal (he wouldn’t be able to tell us if anything was wrong) and still wears nappies as he can’t use the toilet well so he requires nappy changes. Also if he keeps going and our daughter doesn’t, she will surely ask one day why she doesn’t get to go with her brother wouldn’t she

Now I have a lot of questions and I had no idea where or who else to ask so if you can help me or word me some advice I would be ever so greatful.

How likely is it he would re offend after all these years?
We are doing the right thing in choosing not to ever send our daughter yes?
But should we even be sending our son? Is his excitement and willingness to go, proof nothing sinister is occurring? And is it a worry for our son, like is it strictly a girl thing or is it a child thing in general? (He never touched his sons) Do we bring it up with FIL? And how do I act normal around this man now? I have so many questions!! My mind is just constantly spinning about this now.

I assume they don’t know that we know but when I have thought about it, they never ask when they can take the baby on a holiday like they do our son which I didn’t think much of but it’s either they have always thought we have known (which we haven’t) and know that’s why she doesn’t go or he can’t trust himself and/or doesn’t want the risk.

Sorry this is kind of all over the place, I tried to word it as best I could. We are so shocked and my mind is constantly spinning about this. This kind of thing happens a lot but we never thought it would happen so close to home in our family.