Big stress not needed. Wow... :/
I agree about the talk about rules, chores, expectations...
4 yr old probably needs to stay out of your room, always. Maybe she should get him out of house for at least a couple hours each day. Planning will avoid future awkward stress. And you cannot let the responsibilities all fall on you. And sometimes guests don't really leave when agreed - remember Lia's hellish predicament earlier this year. Horrible thought for me to have to live with, others than my kids, but it has to happen sometimes. How different are the parenting styles?