Yes, I haul hot water for the trough's and also brush them each day to keep their coats from getting matted with ice etc
You should not groom horses when it is cold out. When you groom a horse you break up the little pockets of air and oil that thier winter coat holds for insulation. This inadvertantly alllows moisture to get to the skin and you can cause many skin infections this way as well as cause the horse to be much colder.
I hope you have all this sorted out, It sounds like something fishy is going on with both the ownership and care (or lack of) by the person you think is the owner.
It is a good thing thay have you to make sure they have food and water :)