Hi and welcome to YT
. It sounds like your yorkie is having some aggression issues with the poodle and in general - the mounting and bullying is evidence of this. I'm not great with training about aggression, but hopefully someone here has experience. But I would continue to intervene whenever you see aggressive behavior, and I'd feed the poodle in a safe area for the poodle...don't allow food to be stolen by anybody else. When I feed my 4, I stand right in the middle of the 4 bowls so I can watch them all and so that nobody gets stolen from.