I see they had just the one child Margaret in Scotland and then everyone else is from Ireland... including mother-in-law Margaret Maxwell. Was she not married to Walter's father? Then there is a sister-in-law to Walter named Eliza Falconer...
Lived at Stanrigg, South Row at the time in 1851 as a coal miner. Is it possible he was doing mining in Cavan area during the famine years?