I think I have decided to crate them, individually, with food/water/litter, in the sunroom. Both cats love the sunroom, people will probably only stand out there for a minute or two, any unfortunate events that may happen pertaining to the litter box will be dispersed quickly because of all the screens out there, and best of all, I won't worry that they will get out.
Three questions:
1) Crates are usually barred. Are you sure the bars are close enough that the cats can't escape through the bars? Remember that, when motivated, cats can get through some pretty tight squeezes.
2) Just in case they
do manage to get out of the crates (or have "help" from some visitor's child), does the sun room have a door to the outside? If so, you might want to put the kitties somewhere where there is still a closed door between them and the door to the outside. (Other than that concern, though, the sunroom sounds perfect.)
3) Do your kitties flip out (fear, shyness, whatever) when there are strangers around? If so, perhaps you can cover the crates with a towel or something (leaving the kitties a little peekhole, but covered enough to feel "protected"). Maybe then they'd go into "stealth mode" instead of caterwauling? (You know, that quiet, waiting, watching mode they use when they are watching "prey.") And it might discourage people from being friendly and inadvertently messing with them.
BTW, I went to an open house not long ago where a dog was crated in the mudroom off the kitchen. Seemed to work quite well; he didn't howl or bark, and the visitors left him alone.
Good luck, both with the kitties and with selling the house!