Do you have a friend who could go with you to speak to the owners? I hate to see you give up the enjoyment of being close to these horses. Maybe if you could tell them how much it has meant to you to be able to stop and see them, they would permit the visits. You could be opening the door to a new friendship with the owners. You never know.
As far as feeding...some horses have special diets for their health. Just like people. It is safest to not feed without approval of the owners.
Sometimes a horse can drive you to distraction...other times just quietly sitting and watching them, or standing in a barn listening to them munch hay, or wrapping your arms around that neck and burying your face in the coat is like hugging a big, fat, 1200 pound tranquilizer.
I hope you can continue to enjoy the company of the horses.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger