Pasture Board Arrangements

My brother is in the process of buying 10 acres in rural SE Wisconsin. There are currently 4 horses that belong to a friend of the current owners that are living outside in a fenced pasture. Part of the deal with them buying the house, is that they were asked if the horses could stay there at least 6 months until other arrangements can be made (I have no idea why it would take that long). Anyway, I told my brother that he should have his lawyer write up a contract for the horse's owner to sign. The horse owner evidently is on a limited income, and currently pays no board. Someone from the family comes over daily to feed/check on the horses. There is a barn attached to the pasture. My brother was told that the horses aren't allowed in the barn, but they have been in there on times when he has gone to the house with inspectors, etc.. There is no shelter in the pasture.

Questions for you folks:

What needs to be included in the agreement. It's been a long time since I've had a horse, but I know there were rules, like hours I could be at the barn, but can't remember what else. I told him he'd have to make sure his insurance would cover him if something happens to anyone who comes onto his property to take care of the horses. I told him I thought the horses should have access to the barn, since there is no shelter, his question is then, what happens with all the manure? There isn't that much land to spread it around, and he doesn't want to deal with it, currently there is a huge pile just outside the barn door. Is it unreasonable to ask the people to get rid of it? What arrangements should be made if a horse gets sick or injured, should my brother have their vet's phone number, or should that be up to them. What about access to water in the winter, buckets will surely freeze over. What he originally thought would be a simple thing, might end up being a headache.

Any ideas would be appreciated.
Deb