What is the sufficient intention for making up missed prayers, and is it permissible to make up the Dhuhr or Asr prayers behind a congregation performing the Isha prayer?

The order of missed prayers is obligatory. However, those that have been performed out of order do not need to be made up again, because sequencing among missed prayers is not a condition for their validity. In the future, the order among missed prayers must be observed, whether they are few or many. As for the intention, verbalizing it is not prescribed; rather, the intention for a make-up prayer in the heart is sufficient, and specifying whether it is a make-up or current prayer is not required. It is permissible to pray a missed prayer behind someone performing a current prayer according to the Shafi'i and Hanbali schools, while still observing the order.