See if you can find a vet who will spay the two older ones, remove that teddy, close the room where the eight month old sleeps and start using calming products for them.
Your young cars can't deal with the stress and it's up to you to arrange things so that they are better protected. I don't care that each pair likes to play and besides which, you said each pair sleeps in different rooms anyway. If you don't have doors that you can close to these rooms, use baby gates or temporary screens.
You're wasting time and allowing things to escalate. Your younger cats need your help.
Your young cars can't deal with the stress and it's up to you to arrange things so that they are better protected. I don't care that each pair likes to play and besides which, you said each pair sleeps in different rooms anyway. If you don't have doors that you can close to these rooms, use baby gates or temporary screens.
You're wasting time and allowing things to escalate. Your younger cats need your help.