Which is the correct way to pray Isha combined and shortened behind an Imam who is praying Maghrib, and what are the rulings for the prayer of each of the five individuals mentioned?

Scholars have differed on the validity of a person praying an obligatory prayer behind someone praying a different obligatory prayer. The majority of them hold the view of prohibition. The preponderant view among the Shafi'is is the obligation of completing the prayer for one who prays behind someone who is completing their prayer, and that if one shortens the prayer behind such an imam, their prayer is invalid. As for Ibn Hazm, he permits a person praying one prayer to follow someone praying another, but he obligates shortening the prayer. However, this opinion of his is weak, and the correct view is the obligation of completing the prayer. As for someone who stands for the Witr prayer without having given the salutations (taslim), their prayer is invalid, because release from prayer only occurs through the salutations.