Considering they have a guest room and that you have known them for 3 yrs, I would ask them. What's the worst that can happen? That they can say NO? If they do, then that is okay too.
Some people do not like mixing business w/pleasure.

But from what you tell us, it should be no problem at all.
Just let them know you will be providing your own food/drink/personal toiletries, etc.

Good Luck!!