I've done them alone in a 15 gal
( 24" x 12" x 12" ) but not smaller. Young fish may be able to be done in a 10 but why move the parents if you don't have to? Also, if you plan on letting them raise the babies for a while, you may need the space of the larger tank so the fry don;t kill each other over territory. If this is the case, you may want to do a 20 gal
Hope this helps.