Hi,
I too have a swathe of Ferguson ancestors and relations from Rothesay. I don't have a Susanna or a Duncan as far as I know but I think there were only one or two families of Fergusons in Rothesay and we might connect. I have two Ferguson lines in my ancestry and both lived in Rothesay at some point. In 1869 my great grandmother's parents married. They were Neil Ferguson and Catherine Ferguson. Neil's father Robert Ferguson was born in Bute in 1821. Catherine was from Kilfinan Argyll. Robert's father appears to have been a Daniel Ferguson.
Cheers,
Jan (Adelaide)