Even though they're usually in each other's view, I'd ask the barn manager to try to keep them separate. Don't put them in stalls next to each other and have them turned out in different paddocks or have them turned out at different times. (Are they turned out alone or with other horses?, maybe request to have them turned out with other horses, so they can make new friends). They'll throw fits at first, as you're experiencing, but they'll eventually get over it. All that running around and working up a sweat gets tiring, they'll figure that out eventually. You don't want this situation to get worse.