Update:

• We folded up the cage and put it out on the balcony where they do not go. I figure it might be a stressful sight to both the kitten who was in it, and the cat who is only 1 year old and was constantly on the outskirt of a kitten jail for a month. 1 year olds shouldn't know what jail is.
• We put our cats old kitten harness on the new kitten and his old sweater on top of that. He got the sweater off but the harness (the good kind) seems to be grounding him... a ton.
• We brought out our cats old pop up tunnel.
• We made a huge pet store haul and grabbed: a pop up cube, a battery powered spinner, a battery powered roving laser toy, pheromone spray, calming cat nip, and a roving mouse toy.

Drastic improvements. I think the perches we have now and the 1 manual string toy we had were not enough.

More planned improvements:

• I'm going to order 2 cat hammocks for the windows.
• Going to figure out the best large cat castle for the space we live in so that they can avoid each other when going from point A to point B if they want to be alone.

I had an email drafted to the feline rescue we got him from and thought posting in Reddit first might help. It did.