well, Homer can take a solid beating (the episode where he becomes a boxer and fights Frederic Tatum), and Peter Griffin obviously knows how to kick giant chicken butt (random happenings in a couple of episodes)
So the thing is, who will tire first? And what if they just settle with a drinking contest?
between Meg and Lisa, Lisa has the upper hand considering her intellect. She won't need raw force.
and Stewie vs Maggie. Stewie always tries to make these intricate plans to kill his mother, and ALWAYS fails, whereas Maggie saved Homer from drowning with superhuman strength

It's obvious to mee.
And definitely Bart will kick Chris' ass, no doubt there.
Marge vs Peters wife (can't remember name right now) I'd say marge, because in the episode where she gets mugged and stays inside all the time working out, she probably knows how to punch

and Brian vs Alien: Brian will win. The alien is such a fag