Angels usually ignore euphyllia. They will more than likely chase each other some, but that’s what angels do. This is essentially a modified version of what people do to keep a bunch of African cichlids together. The regal will be at the top of the pecking order, and the others will fall somewhere else.
Any angel would be fine though. Lemon peels can be scrappy as well, but your yellow tang may not like another yellow fish. If you go this route, I would say you are about maxed out in the tank. You will want to monitor parameters and water quality closely. This is just a method to potentially reduce aggression, but you know your regal’s personality better than I do. If you think she would mercilessly attack any new angels or sizable inhabitant, I would reconsider.
Given that some of your fish have some growing to do, I would consider an upgrade in the not so distant future. A 6’ 180+ gallon is what I would suggest. Keeping multiple angels together also becomes easier in larger tanks, and you would be able to add a couple more fish. Your regal would probably be less aggressive with more space too.