The Reddit user known as lostinlightanddark is living the classic chicken-keeper's dilemma, two chicks are practically feathered, two are still fluffy little goofballs, and the thermometer is about to play hardball. Nighttime lows of 40 to 45 degrees are no joke for a bird that's still showing bare skin on its back. Our honest take? Patience is the name of the game, but you don't have to treat your flock like a single unit. Chickens don't care about fairness; they care about not shivering.
Let's talk about those two bigger chicks. At four to five weeks old, with most of their feathers in, they're close to being ready for the coop, but "close" isn't the same as "there." That bare patch on their backs is a red flag. Feathers are their winter coat, and a gap in that coat means cold air hits skin. A 40-degree night with a drafty coop can turn a confident chick into a sick one fast. We'd say wait until those back feathers fill in, or until nighttime lows creep above 50. If you absolutely must move them, add a heat source in the coop, a heat plate or a low-watt bulb, and check on them at dawn. A warm chick is a happy chick; a cold one is a quiet emergency.
As for the younger pair, do not rush them. They are not ready, and pretending otherwise is fowl play with their health. The temptation is to move all four together so nobody feels left out, but chickens do not have feelings about sleeping arrangements. They have instincts about warmth and safety. The little ones still need a brooder. Keep them separate until they're fully feathered and the nighttime lows are consistently above 50. That might mean two more weeks, maybe three. It feels like forever, but a few extra weeks in the brooder beats a lifetime of regret over a chilled chick.
What would we tell lostinlightanddark directly? Move the two bigger chicks only when their backs are fully covered and the forecast shows a string of nights above 45. Leave the little ones where they are. Set up the coop with a heat source for the big two, and watch them like a hawk for the first few nights. If they huddle under the heat plate, you're golden. If they pile into a corner, bring them back inside. There is no shame in chickening out of a cold move. The coop will still be there next week. Your chicks' health will not wait.