But Sue, Fred's answer was really good.
I have three rescues, one male, two females -- they eat separately.. They know when it is their turn and only eat in their turn. When we got them we were told to be careful mixing males, but that females would sort it out themselves. Most of the time the girls will play together fine, sometimes Maude, who has lots of problems, just goes off on everyone and has to be crated.
Zack only gets aggressive when strange dogs invade his territory -- not unusual.
One of the things Joan always used to advise when adding a new rescue to the pack was have them meet in neutral territory and let them sound each other out. It helps no matter what.
Tea