JamesandJon33
Just a little deviation. If your surname is Davies, what is the plural. Obviously it would not have an apostrophe.
I was taught at school, back in the dim and distant past, (the 1950s) that when a name ends on an s, you can use the genitive apostrophe after the s like this: The Davies' house.
My old-fashioned Scottish school-teachers preferred this usage to The Davies'es house, although they had to admit that both forms could be seen in print.
The really old fashioned castigated the -es' form as "baby language" that they were not prepared to accept from nine year old schoolgirls.
We were also taught that James could if he liked, as could Mavis, simply do without the apostrophe and write James book, Mavis school-bag etc. although here too, they sounded disapproving, and that it was courteous to use the form used by the person or institution that had a name ending on s.
Sorry for the digression. The answer to your question is that when we write of the Davies as a family or couple, we simply write, "The Davies are coming for dinner tomorrow."" or whatever they are going or not going to do.
Scottish history talks of the Black Douglas and of the Red Douglas.
If that is all we are told, we are left wondering if this means the two different families or clans, or two different individuals, perhaps the black Douglas the friend of Robert the Bruce and the Red Douglas who , my memory fails me here, either murdered a member of the Morton clan in a bell-tower, of all unlikely places, or was murdered by him.
If any of you still have your copy of Chamber's Scottish History you can find out who murdered whom and where the bell-tower was.