I have always been confused about how you can do something that we all know is impossible, there is no way to transfer a steward in this game to another house that I have ever found, so I think maybe you should think about that and come up with a precise explanation about how you ended up in that situation.
Are you sure you made that person steward of the first house? You were able to order wood and home improvement from them? What was this mysterious dialogue that allowed you to transfer them to another house? Just asking them to follow you to another house does not make them a steward of the new house, they can only be steward of the original house. Take them back to their house, release them and go find another steward for the second house. Chances are they will hang around the second house permanently, but you should never have moved them in the first place, a steward is going to be of no use at another house, you have plenty of housecarls and other followers to help with fighting and being a pack horse. the stewards should be left to look after their assigned house.