If you're married and Jewish, the wife's mother keeps the marriage document, so even if there is a house fire and all documents are lost, your mother in law usually lives in another house, so you can pick it up from there.
I’m married and Jewish. It would be pretty surprising to me if my wife’s mother had even seen our marriage paperwork let alone possessed it. This also isn’t a tradition I’ve ever heard of in my family.
Or did a joke about overbearing mother in laws just go right over my head.
Many might not believe this but Israel and their customs do not represent all Jewry. Israel is the country with the highest proportion of people claiming Jewish roots, but not the country with the most Jews.
I know where my documents are kept. They are not with my mother in law.
You are overreacting to a claim about customs made by one person on the Internet.
The Ketubah is traditionally transferred from groom to bride as it contains his promise to protect her rights.
Under the Chuppah the bride usually wants her hands free for other things and not worry about misplacing the Ketubah at the wedding, so it’s often passed along to her mother, who’s standing close to her, to put it somewhere safe for the evening.
Or did a joke about overbearing mother in laws just go right over my head.