The Old Welsh—and Irish for that matter—used to organise things in threes. Reviving that custom a man could say that one of today's three finest groups in Wales is The Hennessys. they are not brothers, Frank (guitar) is a Hennessy; Dave (mandolin) is a Burns and Paul (banjo) is a Powell. That adds up to two Irish and one Welsh surname. But they are solidly Welsh—and Cardiffian—with a love for Irish folksongs and ballads, in particular.
And this formidable combination of Welsh and Irish is reflected clearly in the range of their singing. They can be lively, rousing, dynamic; equally convincingly, they can be melodious, smooth and reflective. Whatever the song, they are certainly passionately involved: they perform with conviction. This is part of the reason for their success as entertainers, but there is more. There is the respect that each of them has for the other two's abilities and, also, that gift for anticipating how the others are going to sing a given phrase or cadence—a natural sympathy for which no recipe can be given but a feeling which can be developed by constant practice.
The boys certainly have plenty of opportunity to practice. Their audiences, on television and in the halls up and down the country, see to that. So do their friends in gatherings, convivial or otherwise. Introduce them to your own circles; you'll be singing along with the best of them.