I have never heard of such a thing. FMIL as well as my parents, FFIL and FSMIL were all told on Thanksgiving that the guest list has been finalized (has been for quite some time) and invites were being printed etc the following 2 weekends so that they would be ready for stamping and mailing at the end of the December. My parents didn't say anything other than stating that friends who were invited were excited and waiting for the invite to arrive in the mail. (YAY!). FFIL and FSMIL were also excited and left it at that. FMIL seemed excited and didn't say anything at all.
Fast forward to yesterday. FMIL wants to substitute an invite for a family member that passed away over the summer, but what she doesn't realize is that he was married and his widowed wife is still invited. She then also wants to substitute an invite for a family member that has been extremely ill the last month and "Probably won't be better in 3 months for the wedding." First off, how does she know? She doesn't. Invite still goes out. Period. It's part of etiquette. You can't just "add" people to fill in for those that you A) think aren't going to be able to make it, even though you don't really have a clue and

have passed away but have a widow/widower that is still invited. We flat out told her NO to the request. She then said that she feels that she should be able to verbally invite people should we not make our minimum, even though we have told her numerous times that if the minimum isn't met, our single bridal party members will be able to have first dibs on bringing a date. She doesn't like that and thinks that SHE should get first dibs.
FI and I put our foot down with this. Are we right in doing so?