Hi Bill - Samuel Halpin was Robert Wellington Halpin's eldest son. He settled in Drogheda, where he seems to have worked - for a time at least - as a carpenter. He passed away in about 1915 if I remember correctly (I'm away from my desk at the moment, so I can't vouch for the accuracy of my dates).
I believe Robert James Halpin was Samuel's son (the port town of Drogheda, where Samuel settled, is in County Louth).
Samuel had two brothers - Robert and Edwin (my great grandfather). Robert Halpin was born in about 1852, so by the time of the 1911 census he would have been in his late 50s. After Robert Wellington Halpin died in 1883, Robert (jnr) took over his father's responsibilities as Town Clerk. The appointment didn't last long, however, and he practically vanishes from the record after that, resurfacing only twice in a couple of press clippings, which describe him saving a drunken man from drowning (a feat of local 'heroism' that Edwin was to emulate), and some time later as being horribly disfigured in a dockside brawl with another merchant seaman. So it seems Robert took to the sea soon after his father died, while his nephew - Robert James Halpin - became a teacher.
On a final note, Henry Grattan Halpin ended up a Second World War hero for some reason. Will get back to you on that.
As for the actual duties of a "Teller of Stamps" - one of the reasons I posted the document was in the hope that someone might shed light on the sorts of things a Teller of Stamps did to earn a crust. I wonder if an email to the Dept. of Revenue in England would help. Maybe they'd have info on the Halpin mentioned.