Sister lost husband and moving on too soon

[Pipsqueaked]

My BIL sadly passed away 2 years ago. Him and DSis have 2 children now 10 and 12.

After a year my sister met someone new (who seems a really lovely man) and they are now talking about moving in together. My Neices are devastated and say it's too soon.

My sister says she is in love and finally happy again and that the girls love her partner so will come around once they realise he isn't going to.be replacing BIL.

I don't know what to do. Me and sister have never been close (she's a lot older than me) but our parents are really concerned and have said if it's too soon for the girls it should be too soon for her as well. My sister has asked me to talk them round because she says they will listen to me but I don't know what I can do. The truth is I do feel for my nieces. AIBU to stay out of it and let them work it out amongst themselves?

Support your sister by telling your parents it's not their business and everyone will have to act as grown adults. With their own lives.

And the children that her parents are concerned about (and remember this is their only concern - they actually like the man). Do you think the children should just be none of anyone's business? The children can't act like grown ups because they aren't grown up - they are dependent children who have lost a parent and whose lives are ruled by adults. They don't have "their own lives" Telling them to behave like grown ups won't get them far.