A Family Story (Myth?) and Question about Gaelic Languages

[Damion]

SingleMalt's story reminds of what my Grandmother told me about her Grandparents.

She said that they would switch to another language when they didn't want the Grand-kids to understand what they were talking about.

My Grandmother's Grandparents were Cornish miners, from Tywardreath. ...
In the 1860s due to the failure of the local mines they moved to Ardrishaig (near Lochgilphead) then later in the 1860s to Ballygrant (Islay) then to Dalton-in-Furness in Northwest England. Finally around 1880, still following mining jobs, they moved to West Virginia, where my Grandmother was born, in 1896.

The question is, what language were they speaking? Was it

1) Cornish? They were born and raised in a fishing village in Cornwall in the 1830s when Cornish was still being spoken especially by fisher folk.

2) Welsh? It's possible that they worked for years beside Welsh miners in Cornwall and/or Scotland and/or England and picked up a smattering of Welsh.

3) Gaelic? I don't know if Lochgilphead was still Gaelic-speaking in the 1860s but Islay surely was. My G-G-Grandparents might have picked up a smattering during their years there. One of their kids was born in Ardrishaig, one in Ballygrant.

It's highly unlikely Cornish was being spoken in the 1830s. The language is considered to have died out in the second half of the 18th century. Would Welsh miners have spoken Welsh while working? Probably not as English would be the language of work for safety reasons alone. Perhaps they picked up Welsh while socialising with the other miners outside work but that would suggest most of the miners they associated with were Welsh rather than Scots or English.
I think it more likely that they picked up Gaelic being that as miners they would have associated with the common people more who kept the Gaelic longer than the English educated classes. Then again the language they spoke could have been French or Latin.

Were the names of the children born in Scotland Scottish names or generic British ones of the time?