Kahrpistols

Hi! I just recently started looking into touring and have bought a lot of the required gear but still need to make some purchases here and there.

I have two main questions here - I bought a dedicated touring bike for myself and my wife will continue to use her endurance-based road bike (with only a rear rack). I have Ortlieb front and back panniers and I was thinking to use only the top of my wife's rear rack for stuff like the tent, sleeping bags, etc.

First question: Do you think the 60L capacity of my four bags is enough for two people, given that we can pack bulky items on the top of my rack and hers? We are planning to spend some time in the wilderness, away from civilization and therefore shopping etc and some time near cities so we'll have easy access to food etc. I'm not concerned with the latter, as we can buy food regularly, but we may need to store up to a week's (or two) worth of food for two people when we're in the middle of nowhere. Will we run into problems with only 60L capacity for two?

Second: Is it possible to buy one 20L compression waterproof sack for our sleeping bags and to pack two sleeping bags in one compression sack? I believe our sleeping bags (Kelty Cosmic Down 20) would fit in a 10L compression sack, so I was thinking to make things easier to just buy a 20L and use that for both. Would that work?