M.W.
Absolutely set house rules! When kids come over to play, immediately sit them down and give them the list of rules (something like this)
1. Toys must be put away when you're finished playing with them, and before you leave.
2. The refrigerator is for Mommies. If you need something to eat or drink, please ask me to get it for you.
3. Please play in these areas of the house and not these areas.
4. Be nice to each other, no pushing, hitting, mean words or leaving each other out.
5. No tattle tales.
Anyway, let them know if they break the rules they'll be given a warning and opportunity to do it right, and if they can't keep the rules, they must go home immediately.
Don't be afraid to be the "mean mom". You're not mean or unreasonable, but they'll tell you that you are. The guilt of being mean is MANIPULATION to make you do what THE KIDS want. And we all know they don't know what's best for themselves.
Best wishes, stand firm!