Yes. That's it.
You take 1/2 ml for the Brahma (get a marked syringe) and place at base of neck at skin level. It will enter the system and rid your Brahma from scaly leg mite, any northern mites, and a number of internal worms (round especially).
As long as you haven't overused Ivermectin in your area to build up resistance, I find it works really well as a general parasite removal.
You will need to repeat in 10 to 14 days. Then reassess. For severe cases you may need a third or fourth treatment.
As to treating others...it is almost assured you have another bird or two that has it as the mites spread from bird to bird. You may also want to clean your coop, however scaly leg mites stay on the bird rather than in the coop, but a good cleaning of litter and dirty corners would be in order.
I find it easy to treat my flock with Ivermectin. I go out at night while they are roosting. I get a bunch of syringes, pre-fill to the appropriate amount (which rounded for dosing ease is about 1/4 ml for smaller birds, 1/2 ml for larger birds like your Brahma). I fill and put the syringes in my chicken coat pockets, then I literally go through squirting med at the base of the neck or the base of the vent or even in between the wings on the back. Wherever I can access skin level without disrupting the flock. Just be sure to make it to skin level. I can get through my flock of 20 to 24 birds in a matter of 15 minutes or less this way.
There are other ways to treat scaly leg mites, as stated before, but with severe infestations, which your bird has, and with the leg feathering, I think you will find Ivermectin the most effective and less messy.
LofMc