eset is a very good product, a bit better than free stuff. But for the cost, eh.. use MS Security, Avast, Avira Antivir, no worries about buying anything.
As far as the licenses, I don't think you have an issue. What if you had 3 houses with a PC each, does not matter where they are physically, the fact is that it's a "3 computer" pack. Not a "3 computers within 100 feet of each other" pack.