I had a few rare sheep...St. Croix, to help with the weeds. A ram, 3 ewes, and their first round of lambs. They didn't help with the weeds. Instead they browsed trees and shrubs. When my mare was due to foal, I decided that another equine mouth to feed would be helped by getting rid of the sheep. I sold all of them except for one just-weaned little ewe lamb. Nobody wanted her. Her first day alone, she tried to bond with the dog, who wanted nothing to do with her. So she joined the horses, claimed them for her flock, and has been with them ever since. She's long since forgotten that she's a sheep. She does every thing with them, just like they do. She eats with them, naps with them, and, when they go on alert, turning to face some activity over the fence, she turns with them, staring off into the distance with their exact posture. Visitors find this highly amusing.
So I have 3 mares and one ewe living together.
The only experience I have with a mini donkey was with a stud donkey on a ranch I kept my horses at before I moved north. He was smart, obnoxious, and sometimes dangerous. He could be caught, haltered, led, groomed, tied, etc.. He was also an escape artist; he loved nothing more than escaping and leading people, the more the better, on a merry chase around the ranch. He was dangerous with other animals; he killed a few dogs on sight, and thought nothing of trying to mount a mare 3X his size, which happened occasionally when he escaped. He'd stand on two legs, grab the mare's throat with his teeth, and try to bring her down so he could mount.
His worst traits may have been because he was a stud, or because he didn't get all the training he needed. I don't really know.