Hi Merlot
I've not had a go at the 1861 but did look in 1881 to see if I could tell if any were still around. I was wondering if they emigrated...but then I found this one....
Dwelling: 75 Finnieston St
Census Place: Barony, Lanark, Scotland
Source: FHL Film 0203666 GRO Ref Volume 644-10 EnumDist 36 Page 2
Marr Age Sex Birthplace
Neil MC MILLAN M 38 M Campbelton, Argyll, Scotland
Rel: Head
Occ: Engine Blacksmith
Mary B. MC MILLAN M 32 F Glasgow, Lanark, Scotland
Rel: Wife
Occ: Blacksmith Wife
Thomas MC MILLAN U 13 M Dunbarton, Scotland
Rel: Son
Occ: Steam Engine Driver
Mary MC MILLAN U 9 F Glasgow, Lanark, Scotland
Rel: Daur
Occ: Scholar
Neil MC MILLAN U 7 M Glasgow, Lanark, Scotland
Rel: Son
Occ: Scholar
Floria Mc C. MC MILLAN U 5 F Glasgow, Lanark, Scotland
Rel: Daur
John MC MILLAN U 3 M Glasgow, Lanark, Scotland
Rel: Son
Andrew MC MILLAN U 2 M Glasgow, Lanark, Scotland
Rel: Son
Donald MC MILLAN U 1 m M Glasgow, Lanark, Scotland
Rel: Son
Father Neil's age is off...but place of birth fits...and having a daughter named Floria looked like Mom's name. If you're trying to track them forward then this might be a place to pick up some clues......if it's really the right Neil that is!!
Not sure if this helps but best I can offer at the moment
Best wishes
Jean