Social Security Issues: Letter Request on People Living in Household SSI Numbers and Incomes

I received the letter in the mail from Social Security it's asking for my son to report all people living in the household as well as their incomes and household incomes. Why would they need to know my income and my social security number and others living in the house this is for his benefits he's applying for applied for

Social Security Issues: Letter Request on People Living in Household SSI Numbers and Incomes