I've just got married by using the 'force marriage' command on Marcurio, but then when he asked where we should live, it didn't come up with my Proudspire Manor house. Now, here's the thing- I don't know whether or not the game actually recognizes the house as mine, since I used a command to obtain the key, and more commands to upgrade all the inside. This means that I didn't actually buy it, yet I am in possession of the key, I can sleep in the bed, etc. I don't have any mods either. So how do I get Marcurio to move into Proudspire Manor? Does the game even recognize the house as technically mine in the first place?
For the game to recognize the house as your own you need to buy it (it's a script). You can have keys for any number of houses (a key you stolen for example) - the only houses that count as yours are the ones you buy. The "best" way to cheat the system in this case would be to cheat the money, and buy the house correctly.
So, to make the house your own, you should buy it (if even possible, is the house for sale?)