First, double check if he actually qualifies as your dependent. If the living expenses were that high, are you SURE he didn't pay for over half of his own support (the company paid expenses that ended up on his W-2 are considered as him paying it)?
1) Yes. HOWEVER, you may be misunderstanding some things. Although you would not include his income, there are TWO negative effects of that. (1) your "family size" has now changed from three people to two people, which lowers the credit. (2) The SLCSP (column B of the 1095-A) has now been lowered (which will lower your credit), so you need to look up the lower amount and enter that into the program. Below is the link for the Federal Marketplace lookup.
https://www.healthcare.gov/tax-tool/#/
2) Yes.
3) Yes.
