How can one stop masturbating during sleep, and is ghusl required thereafter, and how can one ensure the intactness of the hymen?

The sleeping person is not held accountable, so there is no blame for what is seen in a dream, and no need for worry or obsessive thoughts. To overcome this, strive in supplication. Ghusl (ritual bath) is only obligatory upon the emission of semen that necessitates it. Obsessive thoughts about the hymen are baseless, and we advise you to marry and not dwell on this matter.