Do you have a big wall chart with all the branches that are known listed?
No.
The late Gavin Waddell's book,
A History of the Waddells of Scotland, devotes a chapter to the various Waddell families in Shotts, but even he was unable to find or even suggest any links between them.
I downloaded all the WADDELLS, with all the variant spellings from 1700-1800 from Scotlands People (just the search results, not the images) and put them into a spreadsheet. I didn't do all 96 pages of results, just those from Lanark, West Lothian and a few other parishes. I am hoping to put them in some kind of order that might help find some trees.
You're not the first to do that

It will be very interesting to see if you come to any different conclusions from others who have done the same sort of thing.
The critically important thing to remember is that not all baptism and marriage records have survived, so we can't exclude the possibility that the baptism of Christian Bryce's husband is one of the missing ones.
Also, for instance, The first recorded child of James Waddell and Christian Bryce was baptised in 1765, but there is no record of their marriage, so we can't know whether the five recorded children are the whole family, or just the five youngest of a larger family, and this has obvious implications for the date of the marriage, the dates of birth of James and Christian, and possible names of parents. Nor can we be certain that any hypothetical older children were born in Shotts rather than in some other parish.
See the attached screenshot for details of how defective the Shotts parish register is.
Yes, Swinstie is very likely.