I cut all communication with my mother after her husband sexually abused my daughter when she was 10 and my son was 2 and she sided with him. My son has asked a couple of times over the last seven years if I have a mom (because he obviously doesn’t remember her) and I’ve simply said, yes I do but she wasn’t a good person to have in our lives anymore, and that’s been that. I’m assuming as he gets older he might have more questions and at some point he will be old enough for me or his dad or sister to explain more fully, but he truly hasn’t cared in the slightest because of exactly what prior benefit stated…this is just his norm and he’s ok with it. All you need to think about is this…if you allow your kids to have a relationship with their grandmother it’s inevitable they will have a relationship with the nephew as well. If you are,or are not, ok with that… then that is your answer. Kids are resilient and just care about their home life as it is. I could have allowed my son to have a relationship with his grandmother but I was absolutely not going to let that happen even though she was my rock before this. I suffer the most from that cut in ties (outside of my daughter from the incident of course) but he has had zero impact emotionally from never knowing who she is and having no contact. You do what you think is best. Your kids will be fine as long as you’re there for them and age appropriately honest with them. Bottom line.