First you are dealing with living animals, you don’t get guarantees as far as behaviors. Just because one person did not have problems with two broody hens doesn’t mean you won’t. But the opposite is also true, just because one person did have trouble does not mean you will. Some people on this forum have several hens broody in the same coop on different schedules and don’t have problems. Some people have broody hens sharing the same nest and eggs and don’t have problems. But some people do. We cannot tell you what will happen with yours, but sometimes we can tell you what did or did not happen with ours. You may be fine with them hatching in the same coop, you may not. I really don’t know.
If you isolate a hen while she is incubating, you need to build a cage that she can’t get out of and no other hen can get in. It needs to be predator proof unless it is in a predator proof area. The fencing needs to have small enough openings that the baby chicks cannot get out. You might be able to build a cage around the existing nest, you might need to relocate the hen. In either case you need room for a nest, food, water, and a bit of room for her to go poop. A dust bath would be nice. A broody hen knows to not poop on her eggs but she does not know to not poop in her food or water. You may be doing some cleaning so give yourself access.
If you let the hen hatch with the flock you need to mark her eggs (I use a black Sharpie) and check under her once a day after all the other hens have laid to remove any eggs that don’t belong.
The main advantages with using an incubator is that you control everything. You don’t have to wait for a hen to go broody. But you are responsible for heat, humidity, and turning. You need to clean up after you are finished, more so that after a broody hen. If you have a broody hen you may be able to give her the chicks to raise but you may have to raise them yourself.
The main advantage with a broody hen is that she manages everything. She will probably do a better job than you will. You still have to clean up after the hatch but that’s usually just change out the nesting material.
If you don’t isolate her you need to check under her every day for new eggs. It’s possible a hen will go back to the wrong nest when she takes her daily sabbatical, especially if another hen is on her nest laying an egg when she returns. It doesn’t happen a lot but it is common enough, probably the most common problem. Some broody hens are worse about it than others. The broody interacts with the other flock members. That’s never been a problem with mine but some people say they’ve had problems and I believe them. When dealing with living animals and their behaviors you just don’t know what will happen.
If you isolate a hen you have to work a bit harder in doing food, water, and poop management. If she is isolated away from the flock you may need to do an integration later. If you move her nest she may break from being broody.
It’s not always an easy cut and dried decision. We do it all kinds of different ways for our own reasons. This is not one of those things where there is one and only one way we all have to do it or civilization as we know it will end. I don’t know what the right decision for you is. I don’t know what the actual risk is from two different broodies in the same coop on different nests. There are benefits and risks for every way. I wish you luck!