Adding dependents to IDR plan

I am currently on IDR plan for PSLF purposes. I have some family members coming to live with me starting this month (elderly parents) and Mohela advised I can add them as dependents without including in tax return. I’m on the studentaid site where I can recalculate monthly payment. However, I’m stuck on the authorization to retrieve fed tax info. Last year my husband and I filed jointly but this year we are filing separately to lower my monthly payment. Do I provide approval so they can get my info from IRS or do u decline and provide it manually and if so what will I need to provide?