Congrats, you almost certainly have more in there! Keep them all together. The babies need to feed on the frass of the aduts to gain the bennificial bacteria that allows them to digest wood. If it really looks like it's getting too croded, move them (an all the substrate/frass) into a bigger container.
You can tell males from females by looking at them from the side. Males will look like they have no legs at the 5th or 7th segement (they actually do have legs there, but they are modified to fuction as sex organs and are tucked under.
I would assume all the females are laying eggs. The eggs will be packed in the substrate and would be difficult to find without damaging them.
Other than checking moisture levels and adding food (aka edible substrate), millipedes do best when left alone. One of the things I like about 'em