Home invansion and assault are the charges I would see against those two. At the end of the day,they didn't kill him, Elizabeth did.
Ninja, I agree. Mark will get home invasion, not sure if Elizabeth will since it was never said whether she still lived there (I'm assuming she did), and they'll both get burglary with a deadly weapon and intent to cause bodily harm. Not as bad as attempted murder, but still some hefty felonies.
This is where I wish they had a Law & Order thing to see what would happen with those two,as well as last week's episode. I could see plea agreements for them. The fact Mark didn't kill Elizabeth even though she could ID him will go a long way for him and Meg.
They will do some time for asaault but IMO,Ron was a dead man anyway. Elizabeth simply took advantage of an opportunity to kill her husband and shift the blame on to the perfect scapegoats,two home invaders.