Hehehe. When I read this post I immediately thought of Chris Rock saying "there is NO sex in the Champaign Room!"
All joking aside, In the LTC setting, you're basically working in their home. Sex is healthy, and if they are able to give consent I say let them have fun. It will save you having to give them anxiety medications later on in the shift. You may have to give them something for pain, though!
It's best just to turn around, walk out, and shut the door. The good thing about LTC is you'll know the residents well after awhile, and you'll know who is capable of giving consent.