Fry grow. You may get away with a small tank for a short time but don't count on keeping them in a small tank. The multiple daily feedings do tend to produce about as much ammonia as a single feeding for adults. Fish waste is only a small part of the total ammonia being produced in a tank. With 2 week old molly fry, the female should be no real threat. She may chase a few for a minute or two but will soon decide to let them be if she is kept well fed.