Quoted from "Eledhwen;504417"
Don is correct.
Make sure you have "friended" them and they have the password to house.
Once that is done, they just walk up to the equipment, clcik on the "K" key and begin the process.
I am not sure, but if you had it in a castle before putting it into your house, it might not work.
If you can use it, they can use it is my understanding. Also make sure if you want them to use any storage chests, give them the unlock them.