You don't need to separate them from each other if they get along (aren't currently fighting over eggs or stealing eggs from each other). Chickens are communal breeders - they have an instinct to want to lay together, brood together and raise chicks together as a flock. That's why they tend to all want to lay in the same nest, and ignore all the extra nests you give them, and also why once you have one broody, chances go up others will go broody as well. They are still individuals, of course, so it's possible that some won't get along, but for the most part, broodies aren't a danger to each other or each other's chicks, especially if the chicks hatch around the same time and are the same age.
You also don't need to separate the broodies from the flock. Lots of people prefer to let their broodies raise the chicks with the flock. It's a lot easier that way, because you don't need to house them separately, or do introductions later. The hens integrate the chicks into the flock from the start.
What I like to do is put a chicken wire divider across part of the coop, to separate out the broody in her nest, from the start of lockdown until all the chicks have hatched, just so the other hens don't keep trying to lay in her nest and squish the hatchlings. But that's because my flock is very peaceful and the broodies don't defend their nest - they'll let the other hens sit with them and lay in their nest while they are brooding. Some broodies get very mean and won't let anybody near the nest - if yours are like that, then you don't need a divider. As soon as all the chicks have hatched, I remove the divider, and let the broody handle it from there. Even though mine don't defend the nest, they do defend the chicks after they hatch, so separation isn't necessary after that point.
Right now I have 2 broodies raising chicks together. It started out with 1 broody and a clutch of eggs, but she wasn't doing a very good job, so when a second hen went broody (which is a proven good mother), I kept her on fakes as a backup. Eventually I decided to give her part of the chicks right after they hatched, hoping the not-so-good broody could learn from her. The two hens have teamed up and are raising the chicks together now. For the first few days, the chicks still remembered which mom they were originally under, and kept going back under her, but at this point (2 weeks in), they'll go under whichever, and they all hang out and sleep together as one big happy family. The flock doesn't bother them at all because the moms kick butt if anybody comes near.
I'm in MA, too, and haven't added anything for heat. If the moms are taking good care of the chicks and sleep on the floor with them where the chicks can snuggle under them for warmth, you don't need anything else. I've had chicks hatch in a snowstorm in April (last year) and they were totally fine, out and about exploring with their mom in just a couple of days with daytime temps in the 40s and 50s, nights even lower.
One thing to keep an eye on at night is where the moms decide to put the chicks to bed. When my good broody is on her own, she sleeps on the floor with the chicks when they are young, until they start really feathering out and don't need to be under her as much (they can't all be under her and covered well if they are on a roost, for example, especially if you have more than 2-3 chicks per hen). However, now that she has a "parenting partner", her flocking instinct is overriding her better judgement. She really wants to be with the other broody and chicks as one unit, and the other broody has no good judgement, so good broody will follow her and sleep wherever she settles, even if it's not good for the chicks. For example, bad broody went up on the top roost and left her chicks on the floor (ignoring the very low roost I made for them all where the chicks could reach!) Good broody started out on the floor, but kept looking up, and eventually joined the other one up on the top roost. Somehow she got her two chicks up as well, but the rest of them remained huddled on the floor. Or, bad broody would decide to sleep in a nesting box, good broody would follow, but there isn't enough room in there for 2 hens and 6 growing chicks, so some chicks spill out and curl up on the floor under the nesting box, with nights dipping down to the 50s. So now I have to go out there every night, and pull the broodies down from the top roost or out of the nesting boxes, collect all the fallen chicks from various corners of the coop, and put them with the hens (the chicks go right under, so they still need the warmth). Not saying that this is how it always goes - everything is so very individual - just that two moms complicate things, and the interaction between them can introduce some wrinkles that need human help being smoothed out.
6 out of the 8 still hatched, which is a pure miracle given what they'd been through! But it was very stressful.
They hang out together during the day, sleep next to each other at night, and both hens mother all of the babies.
