Herd Bound?

Quick backstory, I adopted my horse Brandon and his pasture mate Tyler(for my mom)last weekend...they have been adjusting fairly well.
Brandon is 16, Tyler is 23. We have a three stall barn with just one set of crossties. Right now it's frozen ground, we don't have an indoor or even a round pen, just lawn and pasture.

I tried bringing Brandon in to the barn to brush without Tyler and the old retired horse that lives there, and he freaked out. He was calling to Tyler, dancing around, acting afraid.

I brought Tyler in and put him in his stall and Brandon was fine and stood quietly while I brushed him.

I was considering lunging on the lawn for a bit, but I decided against it since it's icy and because of Brandon's reaction to being without Tyler.

Should I just let them get used to things for a few more weeks and hold of on lunging, etc? Or am I giving in too easily.

Brandon is a LOT bigger than what I am used to size wise, and I am a little intimidated. I have been out of horses for a few years before these guys.
I need to get my confidence back and gain his trust.

Any help would be great. Thanks! :)

For now you might want to keep them relatively close to each other. But, as soon as the weather permits, you need to work Brandon very hard, while close to Tyler, and let him rest away from Tyler. Start off with a distance where neither is going crazy, and work your way to resting farther away, a little at a time. Till you can take one away and neither get too out of control. You may want to separate them as well. Side by side, and add a little distance between them, a little at a time. The harder you work him (make him sweat) and then rest away from his buddy, the quicker he will learn, that he always gets to come back to his buddy in the end.

Thank you!