Try handling the RecordExpanded event and closing the tables at that point.
private void gridGroupingControl1_RecordExpanded(object sender, RecordEventArgs e)
{
Record r = e.Record;
if (r != null && r.NestedTables.Count > 1 )
{
r.NestedTables[0].IsExpanded = false;
r.NestedTables[1].IsExpanded = false;
}
}