Yes, you will be considered as one household when you apply for premium tax credits. Note, however, your grandchild may be eligible for Medicaid or CHIP and not eligible for premium tax credits for coverage in the Marketplace. You could of course purchase coverage for her in the Marketplace, but you would not be eligible for a premium tax credit to help pay for her plan if she is eligible for CHIP. For more information, review this guide or check with a Marketplace Navigator for assistance.