Am I sinful and do I owe expiation for reporting a colleague at work who had inappropriate relations with another female colleague, which led to their dismissal? And by doing so, have I caused them to lose their livelihood?

If a young man engages in relationships with foreign women, this is a grave offense, a violation of sacred limits, and an audacity against what displeases Allah. Photographing such acts further exacerbates the matter and spreads immorality. Anyone who obeys him in these objectionable deeds becomes his partner in sin. Denouncing this evil is obligatory, but it would have been preferable to conceal his sin, advise him, and remind him to repent. If advice proved ineffective, he could have been threatened with reporting him to the authorities. Since you have informed the company's officials and both of them were dismissed, you bear no sin, for the decision of dismissal was not in your hands, and you did denounce the evil.