Is it safe to leave your stuff in your wife's house? Or will it disapear in 48 hours like anything in a dungeon?
Doubtful. Any house that is not actually one you can buy and call your own in-game would not be safe. Except for certain exceptions, virtually all houses and buildings reset the items in them eventually.
On a relatively unrelative note, some of these exceptions are:
Helgen Inn: "The ruined inn in Helgen features a wardrobe and an end table that can be used for storage, both of which do not reset. The inn also features a perfectly preserved and functional bed. This makes for a very useful shelter at the beginning of the game, however the fort may spawn bandits if not visited for some time."
Sleeping Giant Inn: The chest in the secret Blades room is safe.
Best of luck.
I wouldn't store anything in your spouses house. After marrying uthguard the unbroken, I stored things in her house. For a little while it worked fine, then one day I came back to empty chests, and all my loot unique items and everything else was gone!!!! On a separate note, any quest items (the type you can't remove from your inventory) remained in the chest. I don't know if this was a glitch or not, but it sure pissed me off