This is a phrase that gets repeated all the time on MN. Now of course it is fine to lay out some basic rules that anyone should abide with such as you clean up after yourself and you don't trash the place.
But "my house my rules" really means - the person who pays the bills makes the rules. But if your adult children live with you, it is their own home too. And I think it is incredibly disrespectful to think that because you are paying the bills, you should dictate to everyone else who lives there exactly what is okay or not okay in their home.
Surely it is basic respect to your adult children to recognise that they should have a voice in any decision making about house rules?