Praise be to Allah.

Firstly: 

There is no doubt that Allaah has enjoined obedience towards parents. Allaah says (interpretation of the meaning): 

“Say (O Muhammad): ‘Come, I will recite what your Lord has prohibited you from: Join not anything in worship with Him; be good and dutiful to your parents; kill not your children because of poverty’ — We provide sustenance for you and for them. Come not near to Al-Fawaahish (shameful sins and illegal sexual intercourse) whether committed openly or secretly; and kill not anyone whom Allaah has forbidden, except for a just cause (according to Islamic law). This He has commanded you that you may understand”

[al-An’aam 6:151]

It was narrated that Abu Hurayrah (may Allaah be pleased with him) said: A man came to the Prophet (peace and blessings of Allaah be upon him) and said, “O Messenger of Allaah, who is most deserving of my good companionship?” He said, “Your mother.” He asked, “Then who?” He said, “Your mother.” He asked, “Then who?” He said, “Your mother.” He asked, “Then who?” He said, “Your father.”

(Narrated by al-Bukhaari, 5626; Muslim, 2548). 

It is haraam to disobey one's parents. It was narrated that al-Mugheerah ibn Shu’bah said: The Prophet (peace and blessings of Allaah be upon him) said: “Allaah has forbidden you to disobey your mothers, to bury infant girls alive, to withhold the rights of others, to demand what is not rightfully yours, to pass on everything that you hear, to ask too many questions and to waste money.”

(Narrated by al-Bukhaari, 2277; Muslim, 593) 

Working for Islam is obligatory upon a Muslim as much as he is able to. Your husband may have to stay in the country to serve the Muslims, teach them and take care of their affairs. Therefore your husband should not go back to his country and give up calling people to Allaah and working for the ummah. A man asked Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him): 

For a number of years I have been teaching people to memorize Qur’aan in a place far away from the city in which my parents live, and they are asking me to stop teaching and work with one of my brothers who live with them. I am hesitant about this matter because I am afraid that if I stop teaching, the students will be neglected and will forget the Qur’aan that they have memorized. What to you advise me to do? May Allaah reward you with good. 

He replied: 

We advise you to continue teaching Qur’aan memorization, because the Prophet (peace and blessings of Allaah be upon him) said: “The best of you are those who learn the Qur’aan and teach it to others” (narrated by Imaam al-Bukhaari in his Saheeh); and because that is in the general interests of the Muslims. You do not have to obey your parents in giving that up, because the Prophet (peace and blessings of Allaah be upon him) said: “Obedience is only with regard to what is good and proper.” But it is prescribed for you to explain that to them in a kind and polite manner. 

And Allaah is the Source of strength.

Majmoo’ Fataawa al-Shaykh Ibn Baaz, 5/412 

Secondly: 

Your husband could obey his parents and return to his country if there is someone who could take his place in working for Islam there and if there is also a need to work for Islam in the country where his family is. In this manner he can do two things at once, fulfilling his father’s wishes and also working for Islam. His own country may be in greater need, and his staying in the country where he is now may not allow him to practise Islam openly or raise his children in Islam.

 But if your husband will be coming back to work in his specialty without working for Islam, then you should be on his side and encourage him to stay and work for Islam. Undoubtedly this will be good for you in religious terms, if not in worldly terms. For what is with Allaah is better and more lasting. We should also note that a person is not like a candle and should not burn himself to provide light for others. If the environment in which he is does not help him to obey Allaah and give your children a sound Islamic upbringing, then try to change it and move to a good environment where your children can grow up in Islam. May Allaah help us all to do that which He loves and which pleases Him. And Allaah knows best.