My great-grandfather was one of three brothers who served, and the only one who survived. He enlisted at 15, the youngest of the three, in 1914 and fought at the Somme and in northern Italy. Unfortunately he died a few years before I was born, but I have most of his medals, and the medals issued to his godfather, who died at Ypres in 1915. One brother died at the Somme (I've been to his grave) and the other's body was never recovered. He's most likely buried among the Germans in one of their mass grave cemeteries.
on my father's side of the family, my great-grandfather was in the 95th Rifles, now the Royal Green Jackets, stationed in Egypt in the years running up to the war. He was wounded early on, as part of the British Expeditionary Force, at the Marne, and returned to fight a year later. He survived, and died in the sixties.
And those are the only ones I know about. It's likely there's more members of my family who served, as my family on my mother's side is huge. Those are just my "immediate" family. Glad that my family has such a storied history when it comes to the great war.