Praise be to Allah, the Lord of the Worlds.
One who travels for a long distance-80 km and more-is permitted to have prayers shortened and combined during that journey once he heads to the destination away from home. If he intended to stay at that destination for four days, in addition to the day of departure and that of arrival, then he is considered a resident. Therefore, he isn`t permitted to shorten and combine prayers once he arrives at that destination. If he does shorten and combine prayers, then prayers offered out of their prescribed time are considered invalid, and the same goes for the four unit prayers offered as two.
Accordingly, it is incumbent on you (Asker and his wife) to make up for the prescribed prayers, Duhr, Asr, and Isha`, for every day that you have spent after reaching your destination. However, you aren`t obliged to make up for the Maghrib prayer if you had combined Isha` with it {Taqdim). This is because you have offered it at its due time and in full form. Similarly, if you have delayed Maghrib to its final moment and then prayed Isha` in its beginning (Ta`khir), then it is considered a make up for that prayer{Maghrib}.
Commenting on the Hadith reported by Ala` al-Hadrami where Allah's Messenger (PBUH) said: An Emigrant is allowed to stay in Mecca for three days after departing from Mina (i.e. after performing all the ceremonies of Hajj)"{Agreed upon}, Ibn Hajar said:"It was prohibited for one who had emigrated from Makkah before its conquest to stay in it. However, whoever went to perform Haj or Umrah was allowed to stay in it for no more than three days after finishing the rituals. Based on this, when a traveler stays at the intended destination for three days, he takes the ruling of a traveller; not a resident."{Fateh al-Baari, 7/267}. And Allah knows best.