advice needed

OK, I have some goldfish that are chasseing a couple of female , in the morning. They are in my outdoor blue tub.  I would love to get some fry so I was thinking of taking what I think are female , putting them in a 55 for a week feed them good with some bbs and then introducing some males for a day or two and then taking all of the adults out.

These are about 2 to 3 inches.

Any advice?

Mark