SCG, what I find saddest is that your well-meaning parents are not helping the dogs, if the dogs believe it is their job to corner someone the humans have clearly invited into their house. Dogs need to know beyond the shadow of a doubt, they are not the pack leaders, the humans are. Any dog that cannot be trusted implicitly should be sleeping in a crate, and in fact should be crated anytime it is not supervised, and on a lead when not crated, until it is 100% responsive to commands, particularly one which has been rescued and has an unknown past. I rescued toy breeds for some time, and even a 5-10 pound dog can inflict a nasty wound if it bites. My position was, any dog that showed a willingness to bite a human should not be placed and should be considered a liability. I put one down when it bit my stepson a second time. Dogs that are so dominant over, or terrified of (most common), humans that they feel they must/should bite them, are miserable beings. They feel they must be on perpetual watch. They can sometimes be rehabbed with training, but it takes a very dedicated soul with the time and energy to do it.
A dog thinks in terms of its pack. If it is not confident the human is in charge, it places itself in charge, and that is when it becomes a danger. Rather than seeking instruction from the human, it makes its own decisions. Short of someone breaking in, it should never take it upon itself to do more than observe the movement of the people in the house, responding when invited to or when habit/training has taught it a response is indicated. A dog that follows you to the kitchen every time you get up just wants to see if it's getting food. A dog that follows you to the bathroom and growls when you try to exit is letting you know you should be afraid, and for your parents to make light of it reinforced the behavior rather than correcting it. I don't mean to speak poorly of your folks, they believe they are being kind to the dogs. Maybe a good gift for them would be, "How To Be Your Dog's Best Friend" by the Monks of New Skete. It's the first book I read on training dogs, and explained how they think in such logical terms.
