I would in all likelihood, just begin as you expect your normal day-to-day to go. Does that make sense? I guess, to put it another way, I would just jump into it. Set your expectations from day one, enforce whatever behaviour guidelines you have, and anticipate the need for a fair amount of patience in the beginning. As Judy said, having the same routine, schedule and rules from day one will make it easier for everyone. Given that they will all be used to you and your home, and kids that age just parallel play, it may not be as bad as you anticipate it to be!!