My nephew told me what his mommy was doing?

i finally comfronted my sister on things my nephew said she was doing lets say it was not good, now she wont talk to anyone she has taken advantage of me and because of my parents i have put my life on hold to take care of them while she went around cheated on her husband and my old nephew saw it all and now he is protecting his brother im so angry cause now they are not alowed to hang out with me they are hurting and it makes me cry evrytime they leave she does not even walk in the house anymore i aske dmy nephews what she was saying about me but they say they dont want to talk about it i can tell there is tension with the oldest (13 yrs old) he has always told me how he hates his mom but now he loves her alot. Im very hurt because i dont know what she is saying to them they never wanted to go home now its like ewhen phone rings they leave like right away not even saying googbye this is really hurting me and i feel like they are being mentaly abused by her shes has always been that way when she was growing up, I have a secret about the youngest nephew who is now 9 she told me when he was a baby and i want to do a dna test on him but i cant bare to tell my parents or him, and it hurts ne because he is like my son she always left them with me when her husband was away. should i do it or not