If your tank is big enough, you can try to place a curtain of plants down, say, the middle of the tank to break up the view of the pair from the other fish. This might help keep the pair's attention on breeding and not defending.
I am currently doing this with a trio(2-F, 1-M) of Angels that formed. The 3 fish spawned once together but have since each spawned separately with the male. Since putting a curtain of plastic plants in the tank and 2 breeding sites on either side of the tank, the 2 females stay on their own side and only interact with each other when one crosses the "line" of plants. The male on the other hand, has free reign of the whole tank. You may want to give this a try before giving up your fish to your friend.
Also, if you are not interested in breeding them, break up the pair and give the female to your buddy or put into another tank. A gender only tank of males will actually get along pretty well if there are no females in the mix. I keep a tank of male only and female only Angels as backups for my breeding pairs.
Hope this helps
