MCMM

This issue has been raised before. The answer depends on who you ask. According to the 8962 it says  "No one can claim you as a dependent on a tax return for 2016."  According to the IRS you can claim dependents or you can elect not to claim dependents. There is no tax code that states you must claim everything you are entitled to. 
 
Some people read the above statement and interpret it as 'if no one claimed you on a tax return - you are eligible' others read it as 'if anyone can claim you even if they dont you are not eligible'. There is no official explanation as to which is correct however the marketplace will give you credits as long as no one claims you, so some people take advantage of that and file/accept credits accordingly. 

I think it depends on can you claim them as dependents or not. If you can - they can't get tax credit.
https://www.irs.gov/...mium-Tax-Credit
You can't get tax credit if someone can claim you as a dependent.
If you CAN be claimed as a dependent by another taxpayer, you must file as a dependent whether you are being claimed or not.
(See https://www.irs.gov/pub/irs-pdf/p4012.pdf)

https://www.irs.gov/Affordable-Care-Act/Individuals-and-Families/Questions-and-Answers-on-the-Premium-Tax-Credit
Look at the last requirement. You can't get tax credit if someone can claim you as a dependent. (it's not whether someone claimed you but the fact that you qualify as a dependent). Please see the link on IRS website.
Who is eligible for the premium tax credit?
You are eligible for the premium tax credit if you meet all of the following requirements:
Purchase coverage through the Marketplace. Have household income that falls within a certain range (see question 6). Are not able to get affordable coverage through an eligible employer plan that provides minimum value (see questions 8 and 9). Are not eligible for coverage through a government program, like Medicaid, Medicare, CHIP or TRICARE. Do not file a Married Filing Separately tax return (unless you meet the criteria in section 1.36B-2T(b)(2) of the Temporary Income Tax Regulations, which allows certain victims of domestic abuse and spousal abandonment to claim the premium tax credit using the Married Filing Separately filing status (see questions 12 and 13). Cannot be claimed as a dependent by another person.