I would recommend getting larger tanks--a 1.5 gallon is not an ideal size for a betta because it is too small for most heaters and the water must be changed 100% every three days or so to keep the ammonia low. Fish in tanks these small often develop neurotic behaviors like glass surfing and tail biting, many become obese from lack of exercise and others die from ammonia poisoning. I suggest getting a larger tank with an adjustable heater. I would not advise a sorority in anything less than a 10G, with a minimum of four individuals.
Personally, if I were you I would take the male you have home and put him in the five gallon--he would be much happier, and wouldn't be subject to the risks of keeping them at work. I've heard horror stories of bettas dying from power outages, overfeeding by co-workers, and poisoning by maintenance people spraying cleaners/pesticides. Something you may want to consider.
As far as personality differences go, I would say that every fish is an individual, although you will likely find that females move around and are generally more active than many males due to their more compact finnage.
Last edited by Adastra; 06-30-2010 at 04:25 PM.