Are you sure they were in Motherwell as early as 1900? No sign of them in the 1911 Motherwell Directory (which was almost like a voters roll) unless they were living in lodgings then, but there is an A. Swarbrick at 104 Shields Road in the 1922 directory. Looking for Nelsons in Lanarkshire is a needle in a haystack job, there is only one Blades in the 1922 directory. William Blades, miner, 36 Thistle Street Motherwell.
I don't think Swarbrick is a local name, perhaps not even Scottish.
Sorry I can't be of more help.
Lodger