Cat advice needed

Our two male cats (12 and 10), as they get older, are fighting more aggressively, with one of them catching more than his fair share of facial scratches and now, what appears to be bites.

The younger cat has always been a more difficult cat, with longstanding vomit issues, and a more distant personality.

We've had the oldest cat 10 years and the youngest one 8. We got the younger one as a companion to the older one, which I have to say has been more a standoff than a friendship.

What are the alternatives I can consider?

I've thought about keeping them in separate parts of the house, but the main level and upper level stairs don't have any sort of barrier. I suspect they'd cope with that pretty well, and would even be able to be together, as long as we were around to police fights.

Thanks in advance for your advice.