First off you should never have a pair of any livebearing fish. They require a minimum of one male to two females. They spawn quite readily, and males will constantly harass females to the point of stress and possibly death. Right now you are seeing territorialness because of the female being in there first. But once the male establishes he will be the boss for sure. There's also a very real chance he will harass your female betta (if these are still in the same tank) as IME male mollies will run a tank. I even had a customer return two particularly large male mollies because they chased and killed her full grown angel fish, within a week.
Secondly, are you sure you have the sexes correctly identified and were maybe not misinformed on the sex of each fish?
Third, once they establish they will spawn roughly every three weeks and you will have tons of babies. You'll need to have another tank or a plan in place for someone to take them. A lot of LFS won't take them because there are simply too many people trying to give them away.
Lastly, you don't have to do anything special. Just have the right ratios, give them good food, shelter and water quality, and then wait. You'll have too many babies in no time.
