I have reasons to believe that my brother and sister were not given a fair chance to properly prove their innocence.
No criminal defendant anywhere in this nation has ever (nor will one ever) been required to prove her/his innocence.
That is NOT how our system functions.
The state, on the other hand, has the BURDEN of proving a defendant's guilt beyond a reasonable doubt.
A criminal defendant is required to do nothing, say nothing, or even enter a plea in her/his defense.
The defendant can simply stand MUTE, and the judge will enter a not guilty plea for the poor soul.
If your relatives agreed to a plea deal, the deal was approved by the judge, the judge admonished the defendant in open court, the defendant being so admonished allocuted in open court about the crime(s), and the plea was formally accepted by the judge; that deal is all but bullet proof.
Criminal appeals are a very specialized area of the law.
MOST convictions are rarely overturned, but all convictions OUTSIDE a plea deal can certainly be appealed.
I suggest whatever you do, DON'T discuss any aspect of your suspicions with your relatives over the telephone, via snail mail, via email, or even in person.
ALL telephonic conversations with inmates are monitored and recorded, as are written communications, and email communications.