assuming she's not legally married, you can claim your grandson but not your daughter as a dependent.
since your daughter works her income probably disqualifies her from being claimed by anyone as a dependent.
if the same situation applied in 2019 and 2020 you can go back to amend those returns to claim HOH.
if you file as HOH for any year where your daughter claimed it, realize she is going to get a tax bill. she'll lose the preferential tax rate and certain credits. however, it was improper for her to claim HOH for the last 6 years because apparently, she did not provide 50% of her son's support
