Will the questioner be sinful if his paternal uncle's wife or the witnesses are prosecuted by the Public Prosecution, and is he religiously obligated to drop the charges so as not to harm them if he feels that the punishment might be greater than their offense?

There is no sin upon you for demanding what is rightfully yours and clarifying the truth. Sin falls upon those who lied, wronged, and sought to unlawfully consume others' wealth. However, the preferable course of action is to forgive and relinquish your claim to alleviate punishment from them, while advising them to repent and fulfill their obligations, as Allah Almighty says: "And the retribution for an evil act is an evil act equivalent to it. But whoever pardons and makes reconciliation - his reward is due from Allah. Indeed, He does not like wrongdoers."