This advice is from the Pet Trainers Association of America....have the other people in the house carry ablolutely fantastic treats in their pockets...all of the time they are home. Find out the Grand dogs favorite, favorite thing and everytime she barks and "alerts" at them they are to throw her treats.
I hope no one takes my comments offensively, but I disagree with this advice for several reasons. I know the intent of the Pet Trainers Assoc. is to build an association for Gwen with people and treats therefore getting Gwen to think; people, treats, people are good. This is good, BUT, the advice that they should give her treats every time she alrm barks is incorrect. If you want to extinguish a behviors you must never reinforce it. In this case, you do NOT want the barking, so you would reinforce her when she IS NOT barking. To build a positive association between the people in the house the first step is simply to build a conditioned reinforcer, in this case, the word "good." No matter what the dog is doing, as long as she's not barking, say "Gwen, good!" then toss the treat. When she whips her head around every time you call her name, you have the basis for obedience work and the groundwork for positive associative reflex arcs in Gwen's brain where the new people are involved.
Also, when you train Gwen, it MUST be out of eye, ear and nose distance from the other animals. I've made this mistake with groups of service dogs. They do get jealous and they will carry on while the training is taking place. When you let them out of their crates, chaos tends to ensue as they investigate all the good things that happened to Gwen when they were locked in them.
ANother thing.......I learned this the hard way, place treats around the house for people to reach rather than on your person ESPECIALLY in a multi dog house. That way two things happen, you save yourself from being attacked by the pack for the treats in your pocket and the dogs can't anticipate when you will and will not reinforce their behavior. They will think you can make food appear anywhere and it makes it easier for training. as for the treats in the pocket, I was using a bait bag for treats when an English Staffordshire Terrior AKA pit bull and two Rotts "discovered" it. It was attached to my belt loop. The pit grabbed the back and began yanking me off the chair, then the Rotts helped him, then they began to bite each other over it. I never unbuckled my belt so quickly in my life, hahaha.
Good luck with Gwen. I hope I've been of some help. Karen Every single time. They will have to do some controling of the other canines in the household(I would have crates for the puppies anyway..my dogs and every dog that visits have their own crates...or have them all on short lines.
I have found that my newest dogs favorite stuff is spiced pork and kept frozen until needed.She is extremely(or was)hostile towards other dogs.. but is ever so much better now. However she is a fussy eater so your Grandog might do just as well with dried liver or some such.
I think that Gwen is stressed, anxious, and unsure where the lines are. She's in a new situation and probably one where there is no clear leader in the group. And her anxieties are overpowering her. I guess it would be wasted breath on your part but some obedience exersizes or trick teaching with each dog in turn so each gets attention and treats all alone would help a lot, along with clear commands and lots of petting for each dog in turn.
Good luck, there are some good books out there for dealing with several dogs in a household where there is conflict. Maybe a good early xmas present? LOL