Praise be to Allaah.
What is required is to
offer the prayers at the proper times, as Allaah has enjoined. Allaah, may
He be glorified, says (interpretation of the meaning):
“Verily, As‑Salaah (the
prayer) is enjoined on the believers at fixed hours”
[al-Nisa’ 4:103].
It is not permissible to
join two prayers except for an excuse that dictates that, such as travel,
rain or sickness. What you have mentioned of being able to pray in
congregation is not an excuse that makes it permissible to join prayers.
Ibn Abi Shaybah (2/346)
narrated that Abu Moosa al-Ash’ari and ‘Umar ibn al-Khattaab (may Allaah be
pleased with them) said: Joining two prayers without an excuse is a major
sin.
Based on that, you should
pray Maghrib at the proper time, then when the time for ‘Isha’ begins,
everyone who is near a mosque should pray it in the mosque, and those who
are far from the mosque may pray it with his brothers, if anyone is around,
otherwise he may pray alone, and he excused in that case.
And Allaah knows best.