Yeah, make a huge extra full fuss of the established Tom, to let him know that he's top cat and still very much loved. The other can still get a big fuss, but not necessarily in front of the established one. I had this on a much lower scale years ago, the older one being used to sleeping on the bed with me at night. The newcomer really gave the established cat the hump. My way of dealing with it was to have the older one on one side, me in the middle and little one on the other side, making huge fuss of both. They seemed to accept this and were friends for nine years until the older one passed on five years ago. Now, having lost the other this summer to kidney failure, we are catless and I'm beside myself...
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me