No. You and your spouse will be counted as a household of two and the income you and he report on your joint tax return will be counted for purposes of determining your eligibility. Your son will be counted separately as a household of one, and his income will be counted separately to determine his eligibility. After the Marketplace decides the amount of premium tax credit each of your “households” are eligible for, the three of you can apply for a family policy offered on the Marketplace and you can apply your combined premium tax credits to reduce what your family has to pay for that policy.