Eviction Process: Roomer

My question involves landlord-tenant law in the State of: South Carolina. My husband and I allowed my son's friend and his wife (and dog) to stay in a spare bedroom when they had nowhere to live. This was a little over two years ago. utilities, furnishings, internet and all other amenities etc have been available all along. We have been more than accommodating all along, even buying them clothes, food, paying for heartworm treatment for their dog etc. Their dog since has damaged things many times and even bit a relative and nothing has ever been done to remedy those things on their part. They stayed here free of charge for over a year because we initially did not ask any rent, thinking it would be a temporary situation. We hit hard times last summer when i had to be out of work for a few months for surgery and finally asked them to pitch in--$50 a week total. A few months ago, they started paying $75 a week total. They usually wait and let it build up about 3 weeks before paying, and we have to ask for it then. There was never technically any 'rental agreement' or lease or anything, just told they needed to pitch in.

Now, there is a major conflict and I want them gone. Immediately. I made this clear 2 days ago. Have been refused to relinquish the house key when I asked for it today, said I will get it when they leave. I said I want them out today and have been told "that's not happening".

What legal rights do I have here?

Eviction Process: Roomer