If you really want to breed bettas you usually need more than one male and one female in the tank as the levels of interest, responsiveness, etc may vary from one betta to another.
Being a group is the best condition for breeding to occur.
Any way I'm linking here a full article on breeding bettas, what is needed and how to do it.
http://joshday.com/howtobreedbettafish.htm
Hope it would help