I have 3 Balas with an Oscar and a Lima Shovelnose, and while they are quite skittish, mine don't seem overly bothered by the aggressive fish. They stay out of the shovelnose's way, but not to the point of running from him. If they want some food that is near him, they'll quite happily go and get it!!!
Having said that, are you thinking of adding all those fish to the tank? if so, I think you're going to have overstocking problems. Balas will grow to over 1ft, so will an Oscar, and tinfoils also get huge and need to be kept in groups, so you're going to have 7(ish) very active fish that all occupy the middle/upper region of the tank that are over a foot long in a 90g tank. That is pretty crowded!!
Just a suggestion, but why not lose the Oscar and Tin foils and get a couple more Balas instead?!!