Well all we know is their testimony. If they credibly confess the Lord Jesus Christ and credibly confess they believe in His Resurrection, then we can't know if they're lying based on what they do or how they behave, although I'd claim 1st John 3:15 KJV as proof positive that if a person is a bona fide murderer (malice aforethought, full knowledge, deliberate consent and all), that if they do confess Christ, then they are lying. But we can disagree on that and still be brothers, just not on that Christ's Resurrection is nonfiction fact of history. That's the sine qua non of the one Christian faith, per Paul the Apostle 1st Corinthians 15:14 KJV.