That's awesome you took them in. Shame on whoever dropped them. They look so sad. They're probably heartbroken at the loss of their hatch/brooder mates.
Brahmas are wonderful. Usually extra sociable and pleasant and easy for beginners. The boys are large and showy and often (not always, but often enough) big teddy bears with nice, low crows because of their size.
It's hard to sex chicks this young, but the jerks who dropped them probably had female chicks to compare them to. With Brahmas, the males' pea combs may have more defined rows and turn pink earlier. They might have different feather patterning, and their feathers may grow in more slowly. There are exceptions to all of these rules, and the signs differ with different breeds.
ETA...I pushed publish too fast: The bottom line is in most cases you won't know for sure whether you've rescued pullets or cockerels when you pick up mystery chicks on the side of the road. Just keep doing what you're doing. Chicken-kind needs people like you! Your setup for them looks great. Since you're in noFla, I'm guessing the garage is at least 50ish? In our house, these littles would be barely feathered enough to be off heat.