Mollies are one of the easier livebearers to look after in terms of the threat from their parents. They will eat crushed flake food and should get some added greens. Even spirulina flake will really help them out. They do best in harder water and if the temporary home you have them in is not a cycled tank, they will need lots of partial water changes. If all that you have in the main tank is mollies, the fry can be returned to live with the parents after 2 to 3 weeks of good food and lots of water changes. If there are other fish in that main tank, it may take longer before the fry are safe in there.