Enoch and Jabez are Biblical names. If you hear a bizarre old-timey name and can’t figure out where in the world it might have come from, the answer is usually the Bible. The other two appear to be last names that later became first names.
I agree. Oliver Sr. was also known as a medical reformer, an author and poet, all of which would have commended him to Conan Doyle: Oliver Wendell Holmes Sr. - Wikipedia. He was better known than his son, the lawyer and jurist, at the time ACD began writing the Holmes stories.
IIRC, this was a joke Hastings made when he discovered that Hercule Poirot had a brother named Achille.
Although it’s not completely clear in the Poirot novels whether Hercule really had a smarter but less ambitious brother named Achille or whether he was himself making a joke based on Sherlock and Mycroft Holmes.
The Agatha Christie Ltd. site seems to be down right now, but here’s the Google cache of their page on Achille Poirot. (It contains major spoilers for The Big Four and Curtain.)
Do we know Sherlocks parents names?
I thought the non-canon Seven Percent Solution might venture a guess. No dice.
In hindsight, I missed a chance to say “Sarah and Eben”. Oh, well…
No, Conan Doyle told us nothing, really, about Holmes’s life before he met Watson. Fertile ground for speculation, but no hard facts to work with.