Hi,
Under the new rules, it is not necessary to submit specified evidence of accommodation. If you were granted your fiancee visa under the old rules then evidence will be required.
Your tenancy agreement should be fine or, if it's an information arrangement, a letter from your husband's step father confirming that he owns the property, is happy for you to live there and confirming the number of bedrooms and living rooms in the property. A copy of his mortgage papers and/or Land Registry papers would also help.
If you're unsure, you could take these documents with you just in case they're asked for. It's unlikely that they will be though.