I do not have permission to post pictures, so I won't in order to protect the innocent
We started the underweight horses on free-choice hay when not able to graze. They're still on the same grain regimen, but soaked beet pulp has been added twice daily. The one mare is almost to her ideal weight, the other is still underweight but has gained. I have to remember that saddlebreds always look leaner than the stock-type horses I am used to working with.
We are working both mares more consistently (light work, not overworking - some lunging, ground driving, long lining, light riding) and they are gaining muscle as they fill out. The mares were wormed last month and will be wormed again soon. They still need their teeth floated and the owner is currently working on getting the money available to get teeth done.
The mares were moved next to each other. They were previously both next to geldings, and were in heat and pacing the stalls. Since being moved away from geldings, this behavior has pretty much stopped and their cycles have evened out. I think this helped, they're not constantly moving around nervously.
The gelding was adopted, and gained a good bit of weight with the new owner.