As others have said, you do not qualify for Head of Household (HoH) filing status, unless you are claiming a dependent.
Q. How do I get Turbo Tax to understand that I would like to claim Head of Household without claiming a dependent?
A. You can't do that. If you do not plan to claim your grandson, as a dependent, you should not enter him in TurboTax (TT). The interview is designed for divorced and separated parents, who can do something like what you want to do. But a grandparent can't do that.
That said, a child can be the “qualifying child” dependent of any close relative in the household. So, your daughter could allow you to claim her son (instead of her, not in addition to) as a dependent. That would allow you to claim HoH, EIC and the child tax credit, instead of her. It may be worthwhile to prepare tax returns both ways to see which way the family comes out best. This tool may be helpful.
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
There is one caveat, to qualify to do that, your AGI must be higher than your daughter's.
