(1) Is it allowed to pass in front of muqtadi while performing prayer in congregation? Please note that the person who passed in front of muqtadi came and performed prayer besides imam due to lack of availability of space.
بسم الله الرحمن الرحيم
It is sin to pass in front of the namazi. It is mentioned in hadith: If the person passing in front of the namazi knows its sin, he may wait up to forty years.
لو يعلم المار ماذا عليه من الوزر لوقف أربعين خريفاً (بزار)
If any person is offering salah in a small mosque then one should not pass in front of him no matter if there is a long gap. But if the person is offering salah in big mosque or in field then one should not pass from the place which the namazi can see while his eyes are in sajdah place i.e. nearly the gap of three safs or four or five yards. If someone is offering salah on any passageway i.e. on platform then one should not pass within the mark of sajdah. (Fatawa Mahmoodiya 11/178 Meerut New Edition)
Yes, if there is a sutra i.e. column etc in front of the namazi then there is no harm in passing by. Likewise, it is also allowable if one is not passing in front of namazi rather slips away from his right or left side.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.