I can answer this with a fair amount of certainty in that the Watersons only came to the Sheffield carol tradition in the early 70's or maybe even later.

Martin and Norma used to come on a regular-ish basis and I can remember them bringing the young Eliza about ten/fifteen years ago. The last time I can remember Martin and Norma at the carols was the year the National Lottery started.

Mike I know has never been and each year I invite him. I am 99% certain that John has never been either.

Before John Harrison sang with the group Pete Ogley was a member and he was a particularly good harmony singer - I am sure he had some influence. He went on to join Cockersdale.

In fact the Watersons did not sing what is generally regarded as harmony - they sang the notes they felt like singing and this has some strange results.

Listen to Yorkshire Garland and Mike does a harmony on the line "Helmets glistening in the sun" (Side two first song as I remember) only on the first verse. He never ever repeated it either on the record or in real life as far as I know but it is is thankfully captured. That did happen from time to time on other songs and Lal was especially good at it.

But in answer to the question they were not influenced by the carols as such. The biggest influence was probably Bert Lloyd - but the singing was (and to my mind still is) unique.

Dave