This is just me, but I’d wait a couple more weeks to see if the others in veg start to flower automatically (most auto’s will flower after 3-5 weeks)
If they don’t start to flower in a couple weeks, then they are for sure photoperiod plants and will need the 12/12 flip to start their flowering.
I’d still wait a few weeks either way to flip if they are photos, they could get a bit bigger/bushier before flowering, otherwise they won’t produce much.
If they are photoperiods, you can veg them until you harvest the one in flower, and then put them in 12/12 to start their flower, or,
find a new spot for either the ones in veg to start 12/12, or a place for the one in flower to stay in the 18-6.
I only recommend this because auto’s really don’t like to change from 18-6 to 12-12 halfway through flower