I think you are probably busy with the little one....
I've gone back and double-checked, it was Alexander's 1846 marriage cert that showed father as Alexander, a mason.  I have checked the 1841 Scottish census so often that I think I know all the Kirkcudbright McMinns of by heart now! Nothing obvious showed there but as we all know, with transcripts for indexes there are always potential misses....Just thought to check the 1851 census and this is the entry that I have found:
Alex McMin 65, mason, b. Borgue  Twynholm, Kirkcudbt 
Mary McMin 66, b. Kirkmabreck, Kirkcudbt 
Isabella McMin 25, daughter, b. Borgue, Kirkcudbt 
James McMin 13, grandson, b. Gatehouse, Kirkcudbt 
Address: Knockmuck, Borgue, Kirkcudbright