You could always divide the ten gallon tank--it would be the safest thing and, in my opinion the best thing for a novice to do. In my opinion, keeping females together is really something an experienced betta keeper should do. Often females in a sorority situation can get injured or they show too much aggression to be kept with the other females--someone who keeps a sorority needs to know how to deal with injured fish and how to gauge when a female needs to be removed due to behavioral incompatibility. Some females are just as aggressive as males, and can't cope with a social situation--when you decide to form a sorority you are accepting that there is a risk that some females may be incompatible, and that in this case it is your responsibility to maintain these fish in a separate tank where they will be alone.
I highly suggest dividing the tank into three sections, one for the male, and one for each female. This will keep all of the fish safe and won't overstock the tank. You will have peace of mind that you won't wake up to a bunch of dead or injured female bettas, and you won't have to worry about keeping the male in a separate tank that you would have to maintain.
There is a tutorial on this site about dividing a tank using craft mesh and report binder spines--I have done this myself and am very pleased with the results. It is very cheap and easy.
Last edited by Adastra; 08-01-2010 at 06:37 PM.