Yes, make sure the 3 gallon is fully cycled and has a filter (sponge) and add plants for shelter. You may need a heater as temperature fluctuations would stress the fry.
There really isn’t much of a need to separate them as long as you have somewhere for them to hide, like plants. In my 40 gal I have a pile of rocks in the corner and the fry drop down into it and then in a day or two they start to come out.