Very little info can be gleaned from the video. Horses look groomed, well fed, healthy. It's rainy/muddy so if they're dirty right now, they probably rolled in some mud, no big deal. The one kicking the fence looks alert, no signs of distress, probably wants food or to go do something, perfectly normal behavior and pretty tame as far as boredom behaviors go. The one behind grabbed some hay it looks like. Horses biting eqch other is perfectly normal, though I personally would keep one separate if it regularly picked fights and the other horses didn't have room to move away. Can't tell how big that enclosure is. You ideally want a minimum of 10x10 space per horse (living condition), but if they cluster themselves up in a corner, that's on them, and if you have something smaller for short term, that's not necessarily an issue by itself. Depends on the citcunstances, which I can't tell from this video. There doesn't seem to be a lot of manure given the number of horses (again, hard to tell from the video) so the owners likely muck out regularly. There's no problem for horses stepping or standing in poop if there is no other option, as long as they're cleaned regularly.

Giving pony rides isn't a shitty thing to do in and of itself. Based on this video alone, I can't call this abuse. I would need to know long term treatment.