Children invited to party parents not.

I have a manipulative sister in law, who within an hour of burying there Mother, started a huge fight with with my husband and some how " blames me" not sure what for, Because I told my husband if she only said bad things to say about me that she needs to speak with me, not him. Over a year has passed my other sister in law keeps passing messages to my teen children from there aunt.
I have told this aunt to please not do that,,, it has continued,
we where not invinted to a bridal shower, and wedding... and now only my two childeren on 18 and one 15 are invited to a college graduation party, via written invation with reaply card.
and the other sister in law told them to look for the invitation.
I don't want my kids to drive two hours away for a party at 4pm
and to spend time with people that hate us. My kids don't want to go with out there parents. How would or should I reply?