Barking from a car is more common than you might think. They're in their territory that they need to protect, but unable to do anything about it (cooped up). So it can be a stressor for dogs prone to some anxiety.
One of the things I like to do for dogs that have anxiety issues is take them away from all the other dogs -- away from the house is preferable, but at least, in another room where we're not disturbed. And I teach them tricks. Yep. Happy silly tricks. No stress. Nothing too practical. I don't use the word "no." Just me, a load of snacks and one or preferably two tricks that we'll work on that day. Play Dead (or we call it "take a nap" at my house). Roll over. Shake. High Five. You can buy a book or dvd. I'm sure there are You Tube videos as well.
This accomplishes a couple things. First, it's mental stimulation. Your dog is learning something. Second, he's gettting one on one time with you, but it's not overly emotional gushing time (that can actually contribute to anxiety). It's happy time that's being earned. Three, throughout the day, you shout out to your dog, Wave! Or Salute! and he does it and you toss him a snack (you've taught him how to catch a snack too, right? Without lifting his bottom, right? and if it hits the floor, it's a Leave It, right? Ah! there's three "tricks" right there!).
So he's learning things that he's using throughout the day to earn your esteem as well as treats. The other dogs are noticing this as well (you can bet their watching!). They may even teach themselves the tricks! When you command Sits and Downs, everyone pays more attention to you because you have proven that you give attention and treats. You're the leader. We'll gladly follow you.
My 85 lb adolescent GSD and my 8 lb beagle puppy usually play great together, a little rough, but great. Sometimes, though, it gets too crazy for my taste (SHE usually started it!
). I can tell him "Gentle" and he usually is, for a while, til she starts getting snappy in his face again. But remember rule #1 of training. Don't give a command that you can't enforce. "Gentle" is hard to enforce.
So I don't give that command. I stand across the yard. I then shout, "Camper, Come! Meri! Come! Zamboni (who isn't even involved in the action) Come!" Zamboni immediately runs to me. She knows I have a snack, and she's not doing anything better. The other two look up, realize Zamboni is going to get their snacks if they don't hurry, and they take off running. If they don't respond quickly, I start running, with Zamboni, toward the house, where the big snack container is. THAT always gets them. The best way to get a dog to follow you is to run away from them.
A "Come" I can enforce. I may have to go back and grab the one kid that isn't moving fast enough. I may have to stick a snack at her nose and lure her toward me, or take his collar and bring him into the house. But a "come" I can enforce.
Once they get to me, I can put them all in downs. They can chill for a while. If they were truly out of control, then we'll hang out for a while, and I'll redirect them to the kiddie pool. If they are calm and I think they'll be fine, I'll release them to go back to wrestling.
But I've found that standing there shouting No, Gentle, Leave It, etc does minimal good. I can tell Camper to Wait while I pick the puppy up and remove her from the situation. But eventually, she'll be too big to do that. (And I don't like picking up puppies. I want them to learn to manage themselves on all fours.) I want them to learn that when it's time to stop, it's time to stop. This approach works for me every time. Sometimes, there's a bit of a lag while the wrestlers realize that Zamboni is, in fact, eating their snacks. (I announce it loudly!). Then they run with me to the house at top speed hoping for a snack from the bin in the house! The third dog helps redirect them. Since you have extra dogs, I bet you'll have the same success.