If one set of grandparents is deemed unfit to take custody of the children, would the other set be considerd before placement in foster care?

My grandchildren were removed from their parents care and placed with the fathers parents for the duration of the investigation. The parents just received notice that the children may not be returned to them and the grandparents that have the kids just tested dirty on a drug test. The investigating caseworker told the parents that she would place them in foster care before giving them to any other family. They have never contacted us, we had to contact them. We are willing to take the kids and capable to financially provide for them. We do not drink, do drugs or have anything against us. We do not understand how the children will be placed in foster care before coming to us. If we are willing, being the other set of grandparents would the children be placed with us before in a foster home.