Need help RE: return address on Engagement Party Invitations!

This seems like a dumb question, but here goes:
I made the invitations for our engagement party on my computer, but our parents are the ones paying for the party. I have my fiance's mom as the RSVP contact, since she is retired and home most of the time. Whose address should I put on back flap as the return address? Mine, my parents, or my fiance's mom's address?
And if I use my parents address, do I include both their names on the flap?
Does it even matter? lol.

I would say to put your parent's address since they are the ones 'hosting/paying' for the party.
You don't need to put their names on the flap. Just the address will do.