Will one be held accountable for internal monologues containing blasphemous and lustful thoughts, and does the prayer become invalid if lustful thoughts occur therein, despite attempts to repel them? Is ghusl obligatory when in doubt about a wet dream? And what should one do who suffers from obsessive thoughts regarding purity and the discharge of madhy or wady after istinja', and what is the ruling on delaying prayers due to this?

Obsessive whispering (waswasah) is a disease that must be struggled against and overcome. What you experience from self-talk does not harm you, and ghusl (ritual bath) is not required of you unless you are certain of the emission of semen, which necessitates it. What is discharged after urination is called wadī (a thick white fluid). If you are certain of its emission, wash what has affected you and perform wudu' (ablution). Thoughts during prayer do not affect its validity unless you are certain that something has been discharged. Your 'Umrah will be invalidated if you pay attention to these whispers.