Leon wouldn't know what to do with Ella, but that's cool. He'd probably try to flirt with her a little. If only for the sake of seemingly being very interested in girls.

Frankie is probably someone he just tries to avoid. XD given that he doesn't want to start too much of a problem in his house.

Oh, Mari he'd probably like. She's English, she can relate to things with him. Granted, he's been in the states most of his life, but he still goes back to England a lot for visits.

Charlie XD well, I can see him actually putting up with the stupid if it means he can get his hands on drugs. He might insult Charlie, calling him an idiot...but that's up to Charlie if he puts up with Leon's attitude.

And Sure! I think Leon could get along with Sim. XD He's full of bad habits.