Hi Kaye,
Sounds like Oliver is having fun with your 4 cats!
It is interesting that we have a cat named Oliver and 4 dogs (3 of our own plus a foster dog)!
>We had been using a squeek toy and backed off on that because I was thinking that it might be / somehow ??? making him more aggressive when playing.
I see what you mean but I would say he gets more excited with squeaky toys, not necessarily "aggressive", right?
It is a great time for you to teach your puppy "Leave it" and "Drop it" using praises and treats. This will prevent possessive aggression down the road.
All plays can start with your puppy's invitation (in other words, he can initiate plays) but we humans should end it when he is not behaving well, for example if he keeps pulling the rope hard and ignore your command of "Drop it", you just stop pulling the rope and ignore him. He will soon learn that you are willing to play with him as long as he behaves (this includes not putting his teeth on your skin).
Good luck and enjoy your puppy
