Richard Carrier demolishes that dubious bit of apologetics (link below). There's no reliable record of such martyrdoms, and even if there were, that wouldn't prove the truth of Christianity since lots of people have evidently been willing to die for a lie. That's not at all "highly unusual." Ever heard of a suicidal cult?

We also wouldn't know whether the martyrs could have escaped death by abandoning their Christian faith or why exactly they were killed in the first place.

https://www.richardcarrier.info/archives/9978

See also this back and forth:

https://www.quora.com/What-historical-evidence-supports-or-refutes-the-claim-that-the-apostles-were-martyred-for-their-faith