The guest would sue the property owner if they wish to do so - they are running a business from their home and need to have the necesary protection and insurance in place to allow them to do so. If they don't then they may have some problems....
It also depends somewhat on how the injuries were sustained. For example it it was negligence on behalf of the guest then they may not have a case, or if they broke the house rules and were injured doing so then same applies. An example might be no use of the pool after 11pm due to lack of lighting etc and guest decides to use pool anyway and slips. Well, they ignored the warning.