Oh, so many questions. But first, relax. You’ll be OK.
You might want to read this. She was in Michigan and you are in Georgia. The weather is different, but you can see how she managed in her weather.
You do not need a heat lamp, the hen will keep them warm. One question though, how well is she covering them? If she is not covering them all, the ones that are exposed can cool off and die, then be brought back under her while another one cools off and dies. You usually don’t get good hatches if she cannot cover them all. Also the chicks grow pretty fast. If she has a bunch she may not be able to keep all of them warm. If it were me I’d remove half the eggs and just leave her 8 to work with. That’s enough in winter.
Those eggs can be from either or both hens. A broody hen will try to hatch her own eggs, any other chicken’s eggs, turkey, duck, or goose eggs, door knobs, ceramic eggs, and if she doesn’t have any of those she imagines she does. A lot of times other hens will continue to lay with the broody and the broody lets them. These late additions can’t hatch because she will abandon the nest when the first chicks hatch. What I suggest is to mark the eggs you leave with her, I use a black Sharpie. Then, once a day fairly late, check under her and remove any eggs that don’t belong. As long as you remove them every day they are still good to eat. Just don’t leave them overnight.
If you read through this forum you will find we do these things all kinds of different ways. Instead of letting the hen hatch with the flock like I do, some people build some sort of cage and isolate the broody so no other flock member can get to her nest. After they hatch I leave the hen and chicks alone, hens have been raising chicks with the flock for thousands of years. Others may isolate the broody and chicks from the flock for various lengths of time. Some people tale the chicks away from the hen and raise them themselves. There is no right way or really wrong way, just the way you choose to do it.
If you read that thread above you can see that the hen can keep them warm in a Michigan winter, let alone yours. You do not need that heat lamp.
The multiple rooster question. You are dealing with living animals, there is no clear cut answer. Some people do keep multiple roosters with very little drama. For others it can be a disaster. I think a lot of that has to do with how much space you have but luck is also involved. My general suggestion is to keep as few roosters as you can and still meet your goals. That’s not because you are guaranteed problems with more roosters, just that problems are more likely.
There is another part to that. There are no magic ratios for hen to rooster ratios that guarantee success or guarantee failure. But it is better to have more females than males. You will often see the ratio of 10 hens to one rooster. That ratio does nothing for roosters fighting, over-mated hens, barebacked hens, anything like that. You have one rooster and two hens. Are you looking at a disaster the way they interact? I don’t think so. But I’ll say it again, I recommend you keep as few males as you can. Your odds of having problems drop dramatically when you have fewer roosters. With you one may be the perfect number, especially with just a few hens.
You are exactly right. You have no idea what sex the chicks will be. I hardly ever have a hatch where it splits 50-50 male to female. 2/3 or even ¾ of one or the other sex is more normal and it can be either sex that outnumbers the other. Many people fail to think ahead to what they are going to do with cockerels when they hatch. You can try to let them run with the flock, it’s possible it could work out, but you need to have a plan B ready because you may need it quickly. So what are your options? You could butcher them and eat them yourself, try to sell them but more likely give them away on Craigslist, or put them in a bachelor pad. If you house them in their own coop and run with no females to fight over they normally get along fine.
Breed is a manmade thing. Chickens do not recognize breed, they just recognize me Tarzan, you Jane. Any rooster will mate with any hen.
Hopefully this is enough to get you started. Good luck!