What is the ruling on congregational prayer if the row is not straight, and was there a prohibition against an individual praying alone behind the row, and what should someone who is compelled to do so do?

Straightening the rows is obligatory according to a group of scholars, based on the Prophet's (peace be upon him) saying: "You must straighten your rows, or Allah will cause discord among your faces," and his saying: "Straighten your rows, for straightening the rows is part of the perfection of prayer." If the rows are not straightened, the prayer is valid, but sinful, because straightening is an obligation for the prayer, not within it. As for praying alone behind the row, it is not valid, and the Prophet (peace be upon him) commanded anyone who did so to repeat their prayer.