What is better when the time for 'Isha' prayer begins after Maghrib prayer, while alone in an empty mosque: Should one pray 'Isha' alone in the mosque, or leave to pray it in congregation with family at home, and is it better to raise the Adhan before leaving the mosque in the second case, or not?

If the mosque is the only one in the neighborhood, then its people are responsible for maintaining it, establishing prayers therein, raising the Adhan (definition), and waiting the usual waiting period for congregants. If no one attends, then the worshiper may return to his home and pray in congregation there, as it is better than praying alone in the mosque. However, if there are other mosques nearby where congregational prayers are held, then it is obligatory to go to them and pray there, and it is not permissible to pray alone in the sole mosque if it is possible to go to another mosque where a congregation is present.