If my grandmother recently passed away and her house went to the grandchildren but now we've found out that she has a lot of debt, can they come after the house?

Assuming your grandmother's estate was not probated or administered and she passed leaving a lot of debt, there is the possibility that her estate's creditors may make a claim as to the equity in her former house for payment of the unpaid bills even though the home is to go the grandchildren.

I suggest that you and other members of the family consult with a Wills and trust attorney about the situation you are writing about to see what can be done to assist.