There is nothing wrong, as far as Islam is concerned, that a husband and a wife pray together in congregation especially in places where there are few mosques and people can’t get the chance to pray congregational prayer every day.
Dr Muzammil Siddiqi, former President of the Islamic Society of North America, states the following: The jama`ah or congregational prayer can be performed by two or more persons. The minimum requirement of jama`ah is two persons, an Imam and another person, whether a man, woman or child. It is very good that the whole family pray together, especially in this society where the mosques are so few and most people do not get chance to pray jama`ah every day.
The husband and wife can also make a jama`ah prayer. It is reported by Imam Abu Dawud that the Prophet (peace and blessings be upon him) said, “Whoever wakes up during the night and also awakens his wife and then both of them pray together two rak`ahs prayer, their names will be written among ‘those men and women who remembered Allah most’ (referring to surat Al-Ahzab 33: 35)”
If there are two males praying together in jama`ah, then one of them will be the imam and the other person should stand one step behind at the right side of the imam, but if the husband and wife are praying together then the wife should stand behind the husband.