As far as I'm aware Thomas's first wife was Agnes Johnson.I haven't come across any Barbours/Barbers in relation to the Maclean family.
I do have baptism details for the children of William and Sarah MacLean in NTH but I'd imagine this Sarah is too old to be the one you're looking for.
Fred's father was actually maried 3 times; there was a wife between the one whose children you've mentioned and Martha Jane (my great grandmother). He had 3 children with his second wife: Isabella, John and Samuel Corkey.
He and Martha Jane had 12 children, the 3 you haven't mentioned are David, Elizabeth and Wesley.
Alexander died in 1906, which I believe is the reason for Martha Jane going to America. She came back in 1912 with my granny, also named Martha Jane.You might have known her as she had a shop in Newry Street; her married name was McConnell and she died in 1998.
I have a copy of the 1910 census and, while I'd noted that there was a boarder, it never occurred to me that there may be some connection.
I'll see if I can find out anything more about a possible Barbour connection and let you know.In the meantime, if you need anything more about the MacLeans let me know.