There are a few things you can do to attract the most people to your ads and have them follow through with their interest.
1. Clean them up! Give them a bath, trim those feet, brush that hair, and put on a nice clean halter and a nice lead rope. Do not have them stand in muck. A nice grassy area with a background that does not distract the eye. You need confo shots, especially for brood mares if that is your selling point. Make them stand square and take pictures from all angles. This would be a great thing to do to attract more buyers. A dirty, unkempt horse = uncaring owners.
2. Post their registered names and a copy of their bloodlines. This is also very important for broodmares. Do they have show records? If so, list so. Are they broke? If so, go into detail about how they handle and what they can do.
I won't comment on the breeding quality of these mares as that is irrelevant, but a lot of people feel strongly about people breeding unqualified horses when there are thousands of horses already looking for homes. Good luck helping your friend.
There on the tips of fair fresh flowers feedeth he; How joyous his neigh,
there in the midst of sacred pollen hidden, all hidden he; how joyous his neigh