In summary I located, as possibilities:
a) Name: Edwin Penny Birth Place: Glastonbury, Som. Residence: Devizes, Wilts Death Date: 4 May 1915 Enlistment Location: Yeovil, Som. Rank: Private Regiment: Dorsetshire Regiment Battalion: 1st Battalion. Number: 7338 Type of Casualty: Killed in action Theater of War: Aldershot
b) Ernest Reginald Penny Birth Place: Yeovil Residence: Pontypridd Death Date: 23 Apr 1917 Enlistment Location: Treforest, Glam. Rank: A/Corporal Regiment: Devonshire Regiment Battalion: 1st Battalion. Number: 9933 Type of Casualty: Killed in action Theater of War: Aldershot
1911 census MILITARY establ. PENNY, ERNEST dob 1890 age21 Isle of Wight, Hampshire
but nothing for Silas Walter Penny or Reginald or Frank (gassed)