Ahhh I'm not so great at this stuff, but from what I can tell...
Empoleon is Ice/water
and yanmega is Flying/bug?
Again, i'm no master, but I think possibly finding two other pokemon who could easily defeat your empoleon and Yanmega, might be a good idea for two other members! (or to get even more complicated, find the pokemon who can defeat Empoleon and Yanmega, and then find another two pokemon who can defeat THOSE two pokemon! For example, say a Blissey and a Heatran could defeat your Empoleon and Yanmega, find out what two pokemon can defeat a Blissy and Heatran and have them on your team in case your team is up against them! You'll be two steps ahead of your opponent!)
I'm pretty sure Empoleon is a goner against a Blissey who knows thunderwave and seismic toss.
As for Yanmega, I'd suggest either Skarmory, Heatran or Snorlax might be good choices!
Lucario seems to be a must for many- just in general haha.
For more help, I'd suggest visiting Smogon, look up the pokemon you recieved and it will tell you all the battle stradegies surrounding these pokemon! I hope it helps!