Is it permissible for a wife to pray in congregation behind her husband’s brother, sometimes with her husband present and sometimes without him, and with her husband’s sister or mother present? And is it permissible to pray in the home garden that overlooks the gardens of other homes, knowing that women usually wear the niqab, but do not cover their faces when praying?

There is no harm in a woman praying in congregation with the mentioned man, due to the importance and virtue of congregational prayer. The evidence does not differentiate between the Imam being a mahram or a non-mahram, as long as the leadership of the non-mahram does not lead to khalwa (unlawful seclusion). The Messenger of Allah, peace and blessings be upon him, said: "Prayer in congregation is twenty-seven degrees superior to prayer performed individually." As for a woman praying with her face uncovered, there is no issue with it if she is not in the presence of non-mahram men.