Here is one way you can get at the child table from within the grandchild table.
private void gridGroupingControl1_QueryCellStyleInfo(object sender, GridTableCellStyleInfoEventArgs e)
{
GridTable table = this.gridGroupingControl1.GetTable("GrandChildTable");
if(table != null && table.Equals(e.TableCellIdentity.Table)
&& e.TableCellIdentity.DisplayElement is GridRecordRow
&& e.TableCellIdentity.DisplayElement.Kind != DisplayElementKind.AddNewRecord
)
{
GridRecord rec = e.TableCellIdentity.DisplayElement.ParentChildTable.ParentNestedTable.ParentRecord as GridRecord;
DataRowView drv = rec.GetData() as DataRowView;
Console.WriteLine(drv["Name"].ToString() + " " + drv["childID"].ToString()); //some values
}
}