What Dreamcatcher Arabians said.
I was given this advice when I was having a hard time with my horse being pushed around by three other horses (one of which is a Percheron X so a little intimidating!). Every time I'd go get him, the mare would try to follow him, then the other two geldings would get upset and charge at us and... well, once or twice I just had to let him go so he could get away and I wouldn't get hurt. So I posted a similar question in here and was told to go in there with a whip and mean it! Every time I'd go in, I'd start by pushing the other horses away from my horse. One day, I cracked that whip hard in front of that percheron X (missing him on purpose of course) and he made a big show of kicking up his heels at me and neighing loudly, but ran away. I just kept reinforcing that they were all to keep their distance from me until they just stopped and now leave me alone. If I see one of them starting to move towards us when I'm haltering my horse, I will leave my horse's side and go ape**** waving the whip in front of the other horse until they change their minds. Yesterday I forgot to bring in a while so I just swung around my lead rope. It worked.
I do still sometimes take him out a different way or separate them if I can, because it's easier and safer, but I now know I can go in there and get my horse out safely.