They seem to have moved around as they had a son, William b. Kilmonivaig (near Spean Bridge/Fort William), Inverness-shire in 19th June 1811. No daughters listed for them so far.
Do you have this entry for the 1841
Culachyreach, Boleskin and Abertaff, Invernessshire
Robert Helm, 55, ag lab, b. Scotland
Helen, 50, b. England
William, 30, ag lab. b. Scotland
Catherine Macdonald, 19, Female servant, b. Invernessshire
Janet Irvine, 14. b Invernessshire
Nothing is showing for a baptism for John (1814) - just a submitted entry of his marriage.
Only marriage showing (1800-1811) in Scotland for a Robert Helm was this one:
17 Jan 1806 Eckford, Rox, Robert Helam and Jane Givan.
Maybe Jane died

If Helen was born England (as 1841 census), then it's likely to be in Northumberland. Who were her parents on the death cert?
gnu