First listen to Seraphina's advice. Dying for a cause doesn't make it right nor true.
Next if they where true believers and willing to become martyrs then why would they denounce JC? (Matthew 26, Mark 14, Luke 22, John 18). If they had not they might have been crucified with him, something which a true believer must have cherished?
But more so on the theological side. What is the importance of their martyrship. If JC sacrificed himself for us, then why would it be necessary for the apostles to do the same? Do they detract from JC or add? Is JC's sacrifice not complete unless the apostles do the same? Etc.
Don't let people get away with blind faith and contradicting their own religion.
Then lets see here. If you are talking about the apostles then you are in a load of trouble. You see those who have the most to gain from fabricating their history is also the ones making claims regarding their 'history'. This so much so that obvious fabrications like seeing a similar name in the list of another source would be considered 'evidence' regardless of other sources pointing out that this is a different person.
Its also hard for biblical scholars to actually know the names of the inner twelve or worse the seventy or 120 outer apostles. So its more or less up to church tradition to set the standards. Which is where the martyrdoom comes in. You see we get more tradition when it comes to their death than any actual accomplishments. Because it was a key point for the startling church. Not even orthodox and catholic agree on the list or their fates but somewhat on their deaths.
Now if there truly had been twelve apostles (they replaced judas according to tradition) with the powers as given by tradition their fates going to different countries then it should be well recorded in the countries where they went. They would have been famous. Instead almost exclusively the only sources we have is church tradition and the letters going around the early christians before the church.
Now the only (except for Judas) apostle that are mentioned to die in the official tradition (that later became the bible) is one of the James who was killed by King Herod in
Acts 12. Read it, that is how "important" the death of an apostle is according to the bible. No shining lights, no martyrs angel etc, instead the text focus on getting Peter away from imminent martyrdoom himself.
The rest comes from non-official tradition. So a christian who relies on this treads on the blade between holy ground and heresy. (See the
gospel of Thomas for instance).
Next comes the question why they are twelve at all? Well its because of Mithras. He was turned into a sun god and thus had twelve zodiacal companions. When early roman christianity copied stuff from the Mithra tradition the number of the apostles was copied along that, before then they where more than twelve.
Take st Peter for instance.
Look at
this source, why is it that they claim that his death is in rome is certain while when he died is not? Well its because the sources they rely on contradict each other. Plus all the sources are 2-3 centuries after the fact as usual.
According to one tradition he was ordered beheaded by Nero.
But according to the Clementines text Peter was the first bishop of rome. Which must have been after Nero.
By another tradition he is ordered crucified but refuses to be crucified in the same way as JC and volunteers to be hung upside down.
According to one tradition he dies with Paul, another that he witnessed Paul's death, another that Paul witnessed his death.
etc.
So the most important 'prince' of the apostles fate is unknown even from the church tradition point of view. They didn't bother to write it down. They didn't bother to send letters to eachother regarding his death.
I mean Nero the famous coming anti-christ and prosecuter of christians are only mentioned in Tacitus to have put the blaim of the fire in Rome on christians. If the cults 'leader' would have been caught that should have been big news and written down as well.
Its the worse with the others.
So your problem is that its their tradition, made up in the 3rd cen usually. So it will absolutely cover their doctrine. Therefore go with Serafina's approach or something that is outside of their universe instead.