Hi, Janet,
Sounds like your younger cat has decided to usurp the elder's dominance, and is being successful.
This is a natural progression - it happens in all societies, including human ones!
It is important, for the sake of both, that you do not interfere - do not try to re-stablish the senior as 'boss cat', but reinforce the younger's new status - feed it first, speak to it first and so on. I know it goes all against ones humanitarian instincts, but for peace in the home, you must do it.
Walter