I'm with the posters that say re-investigate the cost of a cruise for 4 vs. land vacation for 6.
However, I have to say I partially agree with your dh on the dinner issue. I would tell the parents what you told us - that you eat out every night. Hopefully they will send enough money for that expense.
But if you invited them already without in the beginning asking for money, then it's too late to go back. My family started letting me take a friend on our 3 week vacation to
Florida every year and that person was treated as a guest - but not a paying guest.
Carnival Elation March 11
Carnival Imagination Sept 07
Carniival Sensation Dec 06
RCI Sovereign of the Seas Sept 06
Carnival Miracle Sept 05
Carnival Glory Sept 04
Carnival Fantasy Jan 04