I would try and find some black mollies that are already SW
converted. Easier on you in the long run and some LFS
may have them. Once the tank/fuge are properly cycled, acclimate the mollies properly as you would any fish. The male/female pair will do the rest
Just be sure you have a decent amount of macro algae for the young to hide from the parents. The adult mollies will also chew on the macro as a food source. If you can put some LR
rubble pieces here and there as it will offer additional places for the brood to grow unhindered.