Tegan's advice and information is spot on. It's irritating that despite the clear notices saying the horses are on special diets, don't feed, so many people continue to arrive with bits of bread, carrot or polo mints, encouraging small children to feed the horses. As has already been said, both ends of horses can be dangerous, horses are unpredictable, flight animals and if one runs, the others tend to follow. They also have personalities, some are biters, some kick out with their back legs. I cared for a huge horse when I was 15 - 17 - he was a horror to catch. We always kept a halter on him to make it easier and carried a bucket of food to encourage him to come close. Some days he simply charged across the field and whichever girl was holding the bucket had to run to get out of his way.
Like everyone else who has worked with/ridden horses, I'm very cautious about walking through fields where horses are grazing. It sounds as though you're walking through a right of way Greyduster so yes, I think the landowner needs to know these two are terrorising walkers. The suggestion of waving a plastic bag is worth a try, horses can see monsters anywhere and tend to run away from them 