You can move them into the large tank safely when they are too big to fit in the largest fish's mouth. If that's before 2 weeks, that's great. If not, you have to move them out anyway, otherwise you risk stunting. Just add some floating plants and hiding places in, and they should be OK.
Feed 4-6 times a day, alternating in flake foods, veggies, and high protein foods, such as brine shrimp, bloodworms, tubifex worms...etc. Keep up on the water changes, and regularly test the water to make sure the water quality is good. Instead of aiming for fine, aim for perfect. You may not get them perfect, but it's a good thing to aim for.