Regulation 9(1)(b) prohibits housing benefit from being paid where a relative of the landlord lives with the landlord:

Circumstances in which a person is to be treated as not liable to make payments in respect of a dwelling

9.—(1) A person who is liable to make payments in respect of a dwelling shall be treated as if he were not so liable where—

(b) his liability under the agreement is to a person who also resides in the dwelling and who is a close relative of his or of his partner;

As it is deemed no payments are liable to be paid to you for rent, no housing benefit is payable.

Please take a look at this article which outlines letting to a relative.