Five months old. It's hard to imagine them still inside. They've been fully feathered for more than 3 months and capable of managing those temperatures. It is time to get them outside.
If the coop has good ventilation and good breeze protection you could probably put them out and they'd be OK. But I don't like probably. I don't know your schedule or your set-up, but I'd put them out every day for as long as you can for a week, whether that is all day or just a couple of hours. Check in on them to see how they are doing but I'd be surprised if they have any issues. But always go by what you see, not what some stranger over the internet like me tells you.
I don't know where you are in the Northeast but from the 10-day forecast (always subject to change) it looks like your temperatures aren't going to be that bad after this current stuff leaves until next weekend. I'd start this afternoon and see how they react if you can, you said the coop is almost finished. They may not like the strangeness of the coop instead of the cold but just see how it goes. I think you will be surprised at how well they manage.