Goodness, I thought you had them together. Now that they are bigger I would put them together. The sucking thing is usually the babies. I really don’t think a teenage squirrel would allow that. They should be past this. As long as they are raised together they should remain friends until release. Are you overwintering? Sorry, I didn’t notice where you are. It would make it a lot easier if they are together.
Squirrels love to play with each other. They roll, tumble and wrestle but I haven’t seen it to be aggressive unless you have a real turd in the group.
The kitchen is the worst place you can let them play. The cabinets sometimes have voids in the kickboard, dishwasher, stove, refrig, etc. I am terrified if a squirrel is in the kitchen and approaches the refrigerator. I fear they will crawl under the refrigerator and get to the back where the compressor and fan are. I have panicked a few times over that. The kitchen is a big no. The bathroom or bedroom is safer. Of course the toilet would need to be closed. You could hang a towel on towel bars, etc for them to climb. A beach towel would be a real delight.
You’re not being paranoid. They can and will crawl into tight spots and get stuck if given the chance. Flyers are smaller but I remember a new flyer (the first day) running under the stove. They dismantled the place and couldn’t find him. A few days later they found his body in the insulation surrounding the oven.
Edit… is that two Critter Nation cages? You can actually link the two cages together and make it a mega cage.