Help! My 10 yr old cat is becoming aggressive.

my mom has 3 cats, all are 10 years old. She has had them since 2001. I have 3 cats, one is 14 and the other 2 I rescued, they are 2 years old.

Lil Darlin is the mom, Thomas and Blackberry are the kittens. These are my mom's cats.

Thomas has become extremely aggressive towards Blackberry, and has started fighting him, jumping on him, attacking him, almost daily with no warning. Blackberry is very frightened, and he does fight back but generally just hides and tries to avoid Thomas.
Last night Thomas got ahold of Blackberry up under a coffee table and we couldn't get them out, and Thomas attacked him so viciously that Blackberry was bleeding in several areas around his face and neck.

Thomas has also started jumping on my male rescue. We have to keep the cats separated now. But it's very hard to do. Thomas won't let them eat, he won't let them go outside, he won't let them inside.

All these cats have been together for years. This just started in the past 3 months.

Also, Thomas has begun spraying everywhere. Especially immediately after fighting one of the cats. He sprays all over the cars, the house, the trees, the flowers, everything.

Also every cat in our house is fixed and has been fixed since they were of age.

We called a vet yesterday after the bloody battle. The vet actually told us we might have to put Thomas down. but I don't want to have to murder him.

My cats are up to date on their shots, but I don't know about my mom's cats. I take care of mine and she takes care of hers.

Mom is waiting on her income tax check to come so she can take all 3 of her cats to the vet.

any ideas what might be wrong??

Is it possible there's an unaltered male roaming outside? It's odd that the behavior would change suddenly, so I'm thinking there has to be a catalyst for his actions. Sometimes an unaltered stray spraying nearby can rile up indoor cats.

well I know my idiot neighbor's cat is a tomcat and not fixed. But Thomas has already attacked him 3 or 4 times and so he doesn't come around anymore.

One of our cats Thomas ran off when she was a kitten, a week after we got her spayed. We still see her around, but she is so skittish now we can't catch her again.