Hi DOC, IIRC you mentioned that because the apostles were martyred, that somehow shows that the Gospel authors wrote the truth.
Now it's been about 300 years since this thread started, so somebody may have already done this - if so I apologise for the duplication.
I suspect that, as has been mentioned ad nauseam, they either wrote the truth as they believed it, or wrote the stories to support their new religion regardless of the truth - to make a point, in other words.
However, if you’re going to use the martyrdom of the apostles as evidence that the unknown authors of the gospels wrote the truth, then I think you need to ensure that the data pertaining to said martyrdom is “real”.
So here’s a summary of what I found on Wiki:
The original team:
Peter: early church tradition says he probably died by upside-down crucifixion in Rome, AD 64.
James, son of Zebedee: apparently beheaded in AD 44 (only recorded in Acts).
John, son of Zebedee: believed to have died of natural causes, aged about 94.
Andrew, Peter’s brother: said to have been crucified at Patras in Achaea.
Philip: According to legend, crucified upside-down in Hieropolis, AD 54. Another legend has him beheaded in the same city. The Catholic
Matthew: Said to have died a natural death either in Ethiopia or Macedonia. However, both the Catholic & Orthodox Church traditions hold that he was martyred - apparently in AD 60 by a halberd.
Thomas: according to Syriac tradition, stoned then killed with a lance in Mylapore, Madras, AD 72.
James, son of Alphaeus: Tradition holds that he was beaten to death with a club after being stones and crucified in Ostrakine, Lower Egypt.
Jude: according to Armenian tradition, crucified in Beirut, Lebanon in AD 65.
Simon the Zealot: from various traditions:
Crucified in Samaria, AD 74.
Sawn in half at Suanir, Persia.
Martyred at Weriosphora in Caucasian Iberia.
Died peacefully at Edessa.
Martyred in Caistor (in modern day Lincolnshire)
Also, killed in a Jewish revolt against the Romans.
Busy, busy, busy, huh?

Judas Iscariot: according to various accounts:
Committed suicide by hanging.
Fell down and burst open.
Stoned to death by the other eleven apostles.
After his body became grossly swollen, crushed by a chariot.
And off the substitutes’ bench:
Matthias: Crucified in Colchis, or stoned & beheaded in Jerusalem. Oh, he apparently also died of old age in Jerusalem.
So the key words, in virtually every case, are “according to tradition/legend”.
According to these data, there’s no real EVIDENCE that any of the apostles were martyred - it could easily be fiction written for religious political purposes.
Many of these stories are also highly contradictory - much like the gospels, eh?

‘Kay?