Is one obligated to fulfill a vow related to two people arriving in a certain country, given that one of them has arrived but the other has not?

A vow contingent on a disliked condition must still be fulfilled if the condition is met and it is an act of obedience to Allah, due to the generality of Allah's saying: "And let them fulfill their vows," and the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him." If the condition is not met, then fulfilling the vow is not obligatory. In this case, since the questioner made his vow contingent on both his and his friend's arrival, and since his friend did not arrive, he is not obligated to fulfill this vow.