Well it's pretty hard to beat them as well as just getting TO them. I would use pokemon with covered weaknesses for example:
-a pokemon that is x-treme tough that you love to battle with and can kick butt
I suggest Torterra knowing: crunch, earthquake, a powerful grass move, and another powerful grass move
-now that you might be starting with torterra, take it a little further with a flying pokemon, just make sure it knows: aerial ace, and I might be a little insane but quick attack, and for the other 2 you can pick I guess it won't really matter
-since you have a staraptor use a fighting pokemon knowing different moves like lucario knowing: dark pulse, aura sphere, dig, dragon pulse
I haven't ever battled the frontier brains (cuz of AR) so I can't tell you what it's like. . . . GOOD LUCK!