My son is 19, disabled and gets SSI how do I claim him as a dependent?

I am having a hard time finding a definitive answer to this.  Our son is 19 and is intellectually disabled.  I am wondering do I click the box that asks about permanent disability?  Also I am having the hardest time trying to figure out how to claim his as a dependent as he gets SSI and pays us Room and Board.  Any help would be most appreciated.

 

Thank you!