Sorry, I should have put this in the last post.
Apparently, Robert and Hugh had many siblings.
Francis b. Aug. 1784 - married Catherine Rose Sept. 1812
Betty b. May 1791
Jane b. Jan. 1782
Anne b. 1787
Elspet b.1783
Janet ( I couldn't find her on the web-site)
So you were right, Catherine married one of the brothers!