McCastlan is one of the harder ones from Canada to trace. To satisfy my own mind I've even gone to the extremes and doubled-checked the various pages of the Relief Fund (Southampton Committee)and as result of my search, nothing about the family are mentioned or confirmed.
However, this particular case may have been dealt with in a different area like London or possibly Liverpool. Both area committee's I've mentioned for the McCastlan case must be treated with a question mark.
Sorry if the above isn't much off a help but I do know of another avenue to explore and once found then I can report back.