To help relations between your cats, I have hear dabbing the back of each cats neck with vanille essence helps.

This makes each cat smell the same and helps them relax. Though I would check this out with your vet first, as I haven't tried this advice myself.

Something else to bear in mind, Inside only cats are more protective of their territory as it is limited to their house.

My cats are more easy going as they also have outside space to play in, now I am not suggest you throw out your cats outside.

But if they had access to a safe outside run and/or you took them for walks on leases, they will become less insecure about changes in their home, like baby kittens in the garage.

If you have the space/money it might be worth a go.

PS. Please may we have more Jupiter & Tinky, Macy & baby photos, we haven't seen enough of them