Anyone know about home insurance? on a house you don't own, but live in?

[SquinkiesRule]

We are going to live in a larger house my mother owns, she is going to live in a smaller house that we (me and Dh) will own, we won't be renters just living in each others house.
How does house insurance work in this situation? Do we insure the house we live in or the one we own?

You each insure the buildings of the house you own but the contents in the house you live in. But you need to tell the insurers about who lives there and check how they deal with that.

That sounds obvious now you pointed it out I'll ask the contents ins people about us insuring the house we buy but Mum will live in. Thanks.