would you be offended (NBR)?

MrsMommyQ

My ILs were over last night and so was 1 of DH's brothers. The 3rd brother is on his honeymoon. My MIL quietly invited DH's brother and his family (wife, 3 kids) over on Monday for a bbq. She also plans to invite the other brother bc he is returning tomorrow. (I overheard her saying all this) She did not invite me and DH and DD. 

In her defense, she knows that DH has to work on Monday from 3-11. However we live 1 mile away from them and DD I will be home on the holiday, having dinner by ourselves.

So, would that offend you? And...we are seeing them tomorrow morning briefly. If she invites us then, what would you say?Would you mention that you overheard her making these plans 2 days ago?