Student Dependent Visa

[Ash2]

Hi there , for student dependent visa, as for as residence documents are concerned I can not provide tenancy agreement as I have been with my aunt since last three years. Although, I do not pay rent but I share living expenses with them ( Gas, Electricity, Telephone and meal ). My aunt has produced me a letter confirming that I am her nephew and she is willing to accommodate my wife and 6 month baby.My aunt family consist of four peoples ( couple and two kids ). She has given me following documents 1) A letter with signature
2) Copy of her passport
3) Copy of one utility bill.
My question is as there is no tenacy agreement between us will above document be suffice ? or what else I should take from her ?. An other thing my wife already lived same address with me twice when she came to UK as visitor.

Cheers