Scottish use of “and them” as a subject

Living in Scotland, I am accustomed to hearing "and them" used in non-controversial constructions such as "We are going to see Fiona and them for Christmas", where "them" is used to refer by concise implication to those associated with Fiona (usually family and friends).

I also know it to be used in more controversial (from the viewpoint of case grammar) constructs such as "Fiona and them are coming here for Christmas"

Diligent online search has only given me one source of discussion:

Quora

Here, one writer opines:

An easy way to figure out which is correct is to drop the “Jack and” and see which sounds right: “Them are going skiing this weekend” or “They are going skiing this weekend”. Hopefully you look at that and recognize right away it should be “They are…”. So, “Jack and they are going skiing this weekend” is correct. (And I think “They and Jack are going skiing…” sounds even better.)

This rule works in a lot of places: Should it be “Jane and me are going to the store”, or “Jane and I are going to the store”? Well, I would never say, “Me am going to the store”, but I would say “I am going to the store"

The Quora opinion seems valid from a purely grammatical perspective and it argues logically from the singular to the plural but it flies in the face of common usage in some of the population, particularly in the west of Scotland.

It is possible to justify the construct by seeing it as elliptical, creating a nominative “Fiona and them” that is composed of “Fiona and (those whom I consider to be associated with Fiona)”. Note that “whom” is appropriately accusative, justifying the construct.

My question therefore is not whether the construct is wrong or right. My question is to ask if others (particularly in Scotland) have significant experience of the idiom.