Their imam does not pray Maghrib in the mosque, so that he can eat iftar at home!

Firstly: 

The Muslim
must fear Allaah and offer the five daily prayers in congregation in the
mosque, unless he is excused because of sleeping, sickness and so on. 

See question
no. 8918. 

With regard
to Maghrib prayer in Ramadaan in particular, there is a great of neglect
concerning it among many worshippers. The imam should be at the head of the
worshippers in this prayer for a reason other than the fact that he is
obliged to pray in congregation; this reason is fulfilment of the trust to
which he has been appointed, or the task with which he has been entrusted. 

If this imam
neglects to pray Maghrib in congregation in the mosque, this does not mean
that you are sinning or that it is permissible for you to pray at home;
rather you must offer the prayer in congregation in the mosque, even if the
imam is not present. Each person is accountable for his own deeds. Even if
he does wrong, you are still obliged to do the right thing and avoid doing
wrong, so as to preserve this ritual which is one of the pillars of Islam. 

It was
narrated that ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) said:
Whoever would like to meet Allaah, may He be exalted, tomorrow as a Muslim,
let him regularly offer these prayers where the call to prayer is given, for
Allaah has prescribed the Sunnahs of guidance to your Prophet (S) and they
(the prayers) are among the Sunnahs of guidance. If you pray in your houses
like this one who stays away from the mosque prays in his house, you will
have forsaken the Sunnah of your Prophet, and if you forsake the Sunnah of
your Prophet you will go astray. There is no man who purifies himself and
purifies himself well, then he goes to one of these mosques, but Allaah will
record one good deed for him for every step he takes, and will raise him in
status one degree thereby, and will erase one bad deed thereby. I remember
when no one would stay away but a hypocrite whose hypocrisy was known, and a
man would come staggering between two others in order to stand in the row.
Narrated by Muslim (654) 

Imam
al-Shaafa’i (may Allaah have mercy on him) said: 

There is no
concession allowing the one who is able to pray in congregation not to do so
unless he has an excuse. 

Al-Umm
(1/277). 

Ibn
al-Qayyim (may Allaah have mercy on him) said: 

Whoever
studies the Sunnah properly will realize that offering the prayers in the
mosque is an individual obligation unless there is an excuse which allows an
individual to miss Jumu’ah prayer and prayer in congregation.   

Then Ibn
al-Qayyim said: 

What we
believe to be the correct view is that it is not permissible for anyone to
stay away from praying in congregation in the mosque except one who is
excused. 

Kitaab
al-Salaah (p. 166)

 Thirdly: 

The way of
the Prophet (peace and blessings of Allaah be upon him) is the best of
ways. He would break his fast with fresh dates; if none were available, with
dry dates, and if he could not find any dates, he would break his fast with
water, then he would go and pray Maghrib. 

It was
narrated that Anas ibn Maalik (may Allaah be pleased with him) said: The
Prophet (peace and blessings of Allaah be upon him) would break his
fast with fresh dates before praying. If there were no fresh dates, he would
eat a few dried dates. If there were no dried dates, he would drink a few
sips of water. Narrated by al-Tirmidhi (632); classed as saheeh by
al-Albaani in Saheeh al-Tirmidhi. 

What this
imam is doing is contrary to the way of the Prophet (peace and
blessings of Allaah be upon him), so you should advise him to come back to
the right path. 

And Allaah
knows best.