Proof of number of people living in a house

[bobby12321]

Hello..
I would really be grateful if somebody could answer my question,

I am in the process of preparing an application for a spouse visa for my wife. We have adaquate accomodation planned for when she comes....and I know that I'm going to need somebody from the local council to assess the (private) property and most importantly certify the number of rooms but...
How do I prove the number of people living in the property and their ages and gender???

Is it a letter from the council?

Thanks.