You should. Because you support both of them financially, you should claim them both as a dependent. Your daughter cannot claim her son as her dependent because she is a dependent herself. (26 C.F.R. § 1.36B-1(f); 26 C.F.R. § 1.152-1; IRS, Publication 929.)
Navigator
Resource Guide
On Private Health Insurance Coverage & The Health Insurance Marketplace
QUESTION
ANSWER