I think you have two choices.
1. Do the cruise. Tell your offspring, this is what's on offer, all are welcome, let me know if you're coming.
2. Choose something else, which maybe all will be happy with.
IN all probability no. 2 will not be possible. Maybe your eldest DS and DIL don't want to cruise, maybe they don't want to go on a big family holiday? My ILs sometimes come up with ideas like this, and DH and I never go. I'm fine with my PILs, and I can handle one BIL at a time, but the whole lot together? Absolutely not! This kind of thing may work for some families, but many other adults don't really want to spend precious holiday time with their siblings.
Your DS and DIL are not being unreasonable in declining the cruise, but neither do you need to accept their suggestion of a villa. You decide what you want and do that, and let them then accept or decline as they wish.