I'll chime in to agree with others that aside from the readied actions, the original poster handled this correctly. (Initiative is not rolled until the encounter actually begins, and readied actions can't exist without initiative.)
One thing I'd ask ... what's so unreasonable about rogues having an advantage in an ambush situation? It's like being perturbed that fighters shine in an anti-magic shell, or that clerics mow down lesser undead like rotten wheat, or that wizards can fireball from 600 feet away. It's supposed to be like that.
Even so, it's not that huge an advantage. First, the rogues do have to win initiative to get the second sneak attack. Second, there's almost no chance of there being a third sneak attack ... in the first round of combat (after the surprise round), the rogues will be engaged. Presumably they'll be dropping their crossbows and drawing weapons, and soon thereafter they'll probably be dead. Third, assuming a fighter's in front, there's a damned good chance the rogues don't even hit with those sneak attacks ... a traditional fighter's AC doesn't come from Dexterity.
If you chivvy a bad-guy rogue out of sneak attacks, you might as well slash the CR of the encounter to something like half what it should be, in short.