Jamaat Salaah and Imaamat

Filling the gap in the saff if the muqtadi leaves during salaah

Q: There is a rule in Bahishti Zewar that it is makrooh to stand alone in a row. The person should pull a person back from the row before him. What happens to the gap formed by the exiting of the said muqtadi to fill the previous row?

If a Muqtadis wudhu breaks during prayer, should he just leave and leave a gap in the saff? What should he do in this regard?

Standing behind the imaam if there are no other muqtadis

Q: I started performing salaah with the imaam and because another person was just there, I stood behind the imaam expecting the other person to join the salaah as well. But that person went to perform wudhu and we completed the whole salaah in this manner.

1. Is my salaah valid?

2. Should I have moved forward to go to the right of imam when I felt the other person will be late?

3. Is moving forward during salah permissible and how much can one walk forward before the salaah becomes invalid?

Performing salaah at home if there is social distancing in one's masjid

Q: With the distances of one meter at the Masjid, some people prefer to perform their salaat in jamaat in other private places (like in a house) with their shoulders together. They perform the five salaat and the jumuah salaat in houses with their shoulders together? Is it correct? Or is it better for these people to come to the Masjid ?