I'd put them all on 12/12 and let them flower. They will continue to grow in flowering and I'm wondering if your two tall plants are going to get too tall for your space. Therefore, it might be smart to cut them back some as they flower. Just consider it an early harvest. Grow the rest out until they're ready, several weeks from now. If you think some are too small for flowering at this point, then put them where they can get light for a longer period. Or yes, you can just kill off the two big ones in favor of the small ones, but you might be able to make something else work.