Many of us are now brooding our chicks outdoors in our coops and runs from the start, using a heating pad system. Please check out the thread on this subject here on this forum. Go back several pages and you will see some very innovative variations of the frame to accommodate larger broods.
I urge you to look into this method of heating chicks as opposed to the heat lamps as a heat source for future broods. But trying to move half-brooded chicks outside when the ambient temps are much cooler than they are indoors where they are presently being brooded is going to stress them. Chickens suffer significantly from wide temperature spreads.
My advice is to keep them all together and finish brooding them indoors, gradually decreasing the temperature where they are to closely resemble what they will encounter outdoors in the coop, then move them all out together when they no longer need any extra heat. This would be when the youngest have all their feathers.
Keeping them all together will avoid the problem of re-integration. That's as stressful as being subjected to temperature variations.