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Alibinshad, you will have to submit HMRC self-assessment statements proving income together with your bank statements + pay slips showing your income from employment and a letter from your employer confirming your salary and terms of employment.
I strongly suggest you read through the information in this link;
https://www.gov.uk/government/uploads/s ... rement.pdf
Who owns the property where you live with your brother or is it rented? If your brother owns the property you don't need a tenancy agreement, but you will have to submit the following:
A letter from your brother agreeing to your wife living there.
A copy of his mortgage agreement, or if owned outright submit a copy of the property deeds.
If the property is rented you will need a letter from the landlord agreeing to your wife joining the household.