You may need to talk with your county property government. First, you need to find out whose name is ***** ***** deed.
Property tax is not a gift. The government may not accept your money. Also, if you pay the property tax without the owner's permission, you may get yourself in trouble. As to the second part, whether you can put a lien on the property, again, you need to ask the County government. However, it is unlikely. To place a lien on the house, the person needs a court judgment, not just a bill or invoice.
However, if the grandchildren's name or trust name is ***** ***** deed, they may welcome the idea for you to purchase the house. To sell the house to you, they may be willing to pay off the current property tax themselves.
Fiona Chen, MPA, Ph.D., CPA, ABV, CFF, CITP