I had a similar case as you with a 2 year old filly and a 13 year old gelding, they were abused by the people I first got so they were really terrified of humans.
First the filly was a bit more easier from not being interacted with for to long of her life, for her all I did was put grain in a bucket and stood beside it and waited for her to come eat, gradually I was able to touch her and she gained trust easily. The gelding on the other hand was a whole different story. You stepped one foot closer and he was gone.
I learned with him, patience. I would put his food down and stand a ways away, after letting him eat a few mouth fulls I would step closer. Of course he would run off but his hunger beat him and he would come back. Repeating this process may be a bit time consuming but once you start something you GOT to finish it. I would do this again and again, staying out there for more then an hour. Wait until I was just inches from his grain and then I would let him be. Soon he actually grew to trust my presence and it didnt' take a long to near him. After you can walk right up to him trust in petting and such is way easier.
Also for halter breaking its a bit more difficult, though you may be able to do that the first time you can get close enough to her. Take a lead rope with you or have it closer to her food bucket so its easy to reach. If you can grab hold of her mane do so and don't let go until you get the lead around her neck, there fore she can't go anywhere. Then, if you want to be harsh about the halter breaking just throw the thing on her face, that is kind of what I did to my foal a few years back, but he was only a month old and a lot easier to hold.