BTW these three horses have only been living together for 2 months give or take some.
Aaah, that may be a lot of the problem. These horses are all adjusting to each other. It takes about six months for a horse to really become "at home" "with the herd" and bonded to you. Right now, they have new things to adjust to AND a pecking order to set straight. I'd be spending some time with the horses each day....one on one as well as with the herd. They each need to see you as the top ranking head right now.
It sounds like you have three horses each trying to figure out where they stand in this new herd. And you may or may not have at least 2 that want a high status. If this is the case, this will cause them to act up, be squealy, kick, buck, etc. And they probably don't want to be pulled away from one another at this point....bonds are being made.
Lead each horse out and away from the fences every day. Lunge them, walk them, whatever, but separate them every day and give each horse something to do. They need to be able to leave each other without a fuss, or this may turn into a herd sour issue. That won't be fun.
Reward them when they leave and work without fuss, do not reward them if they do act up. Little by little they should each come around and know how to come and go without more trouble.
Next time you ride out and leave the hanoverian-arab behind, maybe you can have another person stay back and walk him around on a lead line as you leave....and reward him on the day he allows you to all go without fuss. He will have to eventually learn that he can be alone and that eventually you all do come back. This is separation anxiety, and it can be worked out.