Ron, I am indeed unclear on my ancestors in the Stewart line. I think the Stewart Society site gets me to Ninian Stewart (no. 67), but I'm not sure. I think the line goes as follows:
King Robert II
Sir John Stewart - 1st Sheriff of Bute William died abt. 1465
James died 1477
Ninian born 1460? died 1509?
James Sheriff abt. 1560-67??
Charles born 1618
Margaret Stewart married Petheric McCurdy 1667
This is somewhat sketchy and any corrections or additions would be greatly appreciated.