First off PETA has zero authoritative right to send you a letter threating to take any of your property, secondly if they do show up don't open the door, and tell them were they can go and how they can get there. They themselves shouldn't even be there in general, it should be a uniformed police officer with a warrant, the people making the complaints should not be on the property with law enforcement.
EDIT I just read the post that they did show up and you did just that lol...I get ahead of myself with replies, sorry.