Nice to here you two have much to share, one or both may already know this but it can’t hurt to make sure. May not the family but names are the same.

Checked The Times for Boer War Casualties nothing for Blunsden or Blunsdon so it appears none were killed, wounded or died of disease.

Checked WWI medal index cards on the National Archives web site [orginals available on Ancestry] for surname Blunsd* [* wildcard picking up spelling variants] and single given names and found:

1] Frederick Albert Blunsdon, 2nd Wiltshire Regiment, No 3/385 [CWGC site shows he was KIA when with 1st Battalion]
2] Albert Edward [or Edward] Blunsd* nil returned
3] John Blunsdon, Wiltshire Regiment No 22468
4] Charles Blunsdon, 1st Wiltshire Regiment No 7587
5] Frank Blunsdon , Wiltshire Regiment No 17470, transferred to Dorsetshire Regiment No 46996
6] Arther J Blunsdon, Royal Field Artillery, No 58238
7] As expected William James has no medal index card for the British Army.

All but Frank survived the War.

From the service numbers and medal card returns, looks like at least some of them either were already serving or had reserve [or territorial] commitment at the outbreak of the war.
For any that served in WWI with the British Army, the chances of their service records surviving are very slim [check Ancestry’s search pages] so to check for Boer War service you’ll need to check the Queen’s South Africa Medal Roll and I suppose assume one or more served in the 2nd Battalion Wiltshire Regiment that served in SA. As I previously said as William went to Australia his records should be available in document series WO97 at Kew.

Jeff