How to address this envelope

Can anyone give pointers on how to address this specific situation... we are only doing 1 outer envelope for our invites. My grandmother(divorced), great-grandmother (widowed) and aunt (unmarried) all live in one house all over 18. I’m looking for a way to address their envelope that does not imply my 9 year old niece is invited. Nothing personal but we are having a no kids wedding (venue only seats 30 for dinner) and I’m afraid if I put it to the whole family they will think she can come. Also although we are only reserving 3 seats for them and the online RSVP makes them hand check each name but I’m still worried they will just think she isn’t included on it because she is a child. I put more info in the FAQs section of our website but I’m just not sure it will catch on?!