Again Gerry,
Thanks for your suggestion, I emailed the Catholic Archives, and was astounded to receive a reply back within not even two hours!
They have given me a full list of who is buried in the grave with the two wives, - not my great grandfather Hugh, unfortunately, but we now know of 4 children stillborn or died in infancy, and four "in-laws" buried there! So a very fruitful outcome!
Catholic Archives say they only have records for Dalbeth, and he is definitely not on their records. I understood that the CPR info on SC. People were Scotland wide? So maybe he was buried in a non Catholic cemetery ?? Greenock, where he was drowned?? the search for him continues.
Cheers again!!