No, I don't think so. My husband has a disabled badge but only he is entitled to use it. Contact your local council and report the circumstances. I suspect the widow & daughter are just hoping no-one will say anything.
nope, you don't need permission as they're temporary structures, but they must not be attached to the ground in any way and they must be moved around the field. They must only be used in association with agriculture, not the keeping of horses (if the land is classed as agricultural), so you can graze them there but that's your lot. No jumps or riding round the field.
Just because something isn't attached to the ground doesn't make it exempt from planning permission. it will be a question of fact and degree depending on what you are using them for, how often and if they get moved around or on and off the site at all. You may find yourself the subject of enforcement action if someone complains.