Selby Lamb was also my Great Grandfather x3 so I guess we are researching the same line

All the following info is based on internet searches so can't verify its accuracy unfortunately.
I too have Selby's parents as Alexander Lamb b.1769 & Jean Hogg b.1765, m.1789. Alexanders parents as Thomas Lamb b.about 1739, 04Jan1741 or about 1748 & Isabel/Isabell/Isobel Allen/Allan/Allon b.1745, m.1764 or 1768 (the joy of possible transcription errors and rounding of dates!).
Now its gets a bit more dodgy - have Thomas Lamb's parents as Thomas Lamb and Elizabeth Penmen m.1739. Now if this Thomas was born in 1710 then his parents might be Thomas Lamb and Mary Ker m.1709.
Unfortunately, this information is based on nothing else coming up on the searches I did and with missing records can't really trust this but might give you some names to focus on.
I would be really interested in what info you have after Selby - my lineage is Selby Lamb & Jane - Robert Lamb & Mary Ann Turnbull - John Lamb & Elizabeth LLoyd/Gibson etc, especially regards a supposed marriage between a James Lamb and Jane LLoyd (siblings of John and Elizabeth) that I can't find reference to anywhere.
Cheers.