Okay here it goes. As most of you know I have two female Siberian Huskies. They are inside family members who only go in the yard to potty or play for intervals. At home and in public they are amazingly well mannered and trained. Neither of them howl or bark when someone comes into their own home. Its all wags and running circles. We often go to visit our in-laws for a few days at a time. When we are at my in-laws the dogs have to stay in the yard with their two dogs. My father in-law has the view that only people belong in houses. The older of the two girls, Shiva has taken it upon herself to decide who comes and goes from their yard. She bellows and howls at anyone that's not a family member and at my father-in-law who is very much a family member, but she does not act aggressively and has never attempted to bite anyone for any reason. She has been coming here since she was only a puppy and this behavior has only started in the last year or so. My question is why? Why does she howl at people in their yard and not her own? Is it because she feels less safe because she has to stay outside?

How often do you visit them exactly?
Perhaps they have only just clicked that it is their 'second home' so to speak and that they shold protect it.
Dogs can be very territorial and protective of their family.
My mums great dane is the most lovable doofus of a dog you could ever meet but if anyone tries to open their gate that he doesn't know and he goes off!
We doubt that he would bite anyone that actually came into the yard but if he knows that they aren't family and thinks they shouldn't be coming into 'his' yard then he won't let them in.

Although she has known this place since she was a puppy, maybe she sees this as her place where she goes to "work" so to say! She knows that home is home, and that is where she's most comfortable, because she knows where you are in the house. But when she goes there, she might associate that as her job, because she is not allowed inside, and her job is to protect the people in the house.

Just a thought. It's sometimes hard to figure what they are thinking!