Numerous jamaa’aat in the masjid

What is the ruling about the numerous jamaa’aat [established for the obligatory salaah – taking place] in a single masjid, particularly when some of them pray after the imaam has completed [the first jamaa’ah], and some others intentionally delay [their arrival] until after the imaam [has completed the first jamaa’ah], so they can pray with another jamaa’ah?

When to make up missed prayers

[He] was ill and they did surgery on him; [as a result] he missed a number of obligatory prayers, so is he required to pray them all together once he has recovered, or should he pray all these obligatory prayers at their appointed times, such as [making-up] the [missed] ‘asr [prayer] at the time of the ‘asr prayer, and the [missed] zhuhr [prayer] at the time of the zhuhr prayer, and the [missed] maghrib [prayer] at the time of the maghrib prayer, and so on?