InOzWeTrust, it sounds like you have quite a challenge on your hands.
If the players are arguing a lot, refusing to accept your judgment as GM on the difficulty of the tasks you have defined, then I'd say the bigger issue is that it doesn't sound like they are all fully vested in your position as GM of the game.
The players need to trust in you as GM that you're going to provide a fun game for them. That some tasks will be easy and some will be difficult for your characters, but that most of all you're all working together to have a fun Star Wars adventure.
I'm afraid I don't have much further to offer than just to suggest having a frank discussion with your players. It may be that, as GMs themselves, they feel compelled to adjudicate and to act as rules lawyer.
You need to let them know that if you're playing in THEIR game, you'll be respectful of the work they've done and the effort they're devoting, and that you expect the same from them while you are the GM. As GM you are the host of the party and the director of the film. Edge of the Empire is very collaborative, but in order to collaborate everyone must be working together.
How best to express that to your friends is something only you can judge.