Knowing that you'll probably reject any evidence that I present, I'll go with someone to whom you may give at least a modicum of credibility. Sean McDowell. Sean is one of the most intellectually honest Christian apologists that I know of.
This is a very short video, so everyone should have both the time and patience to watch it.
I'll grant Sean strong evidence for two, Peter and Paul, but for the two James's...ehhh, and from there on the evidence gets a bit more problematic. But suffice it to say that it's unlikely that eleven of the twelve apostles actually died as martyrs.
However, as Sean points out, the important thing isn't whether they died as martyrs, but whether they were willing to die as martyrs. Unfortunately, that's not a very strong argument. A brief look back over history will make it abundantly clear that a lot of people have been willing to die, for a lot of really strange reasons.
But here's an idea, why don't we compare the number of people martyred by the Romans to the number of people martyred by the Catholic church. That should make for an interesting comparison.
Sorry for the snarkiness.