I made a snuggle sack for my 2 girls for lap time. They are very young and so super fast and very nervous, so I don't want them just loose on my lap just yet in case they jump off and hurt themselves (and the cats might get them). Also figured it would make them feel safer. They love it! And they're always in together when it's in their cage. Same with their fleece tunnel - they're frequently inside together. They love sleeping in both the snuggle sack and fleece tunnel. I find the runnel really helpful for moving them - they get scared when I open the cage and so run inside the tunnel. I grab both ends and can lift them up like that, safely tucked inside, and move them to wherever I need to (example another room for floor time). Sometimes I even take them out like that for lap time, then carefully put one end of the tunnel inside the snuggle sack. As soon as I look in the top part of the tunnel they run down into the snuggle sack LoL.
I'll try take a photo of the sack tonight as I'm not sure if it's the same design as what you're talking about. But mine are definitely happiest when in together.