I am from a very conservative (Polish) Catholic family. My father’s job moved us to Utah, where I grew up.
We were the only gentile family in the entire neighborhood. I went to Mormon scouts, played Mormon sports, attended Mormon dances. Everything in Utah is controlled by the church.
Even though we were Catholic, I got along fine. My older sister didn’t - the Mormon boys wouldn’t ask her out on a date.
Just invite their mom to go to Mass with you. It will probably lessen the frequency of her invitation to you accordingly.
If not, put out a “Mormon scarecrow,” like my father used to call our big statue of Mary and invite them over for coffee. They will get the hint from there.