Is it permissible to intend to combine more than one act of worship—such as the Sunnah of Ishā’, night vigil (qiyām al-layl), and fulfilling a need—in two rakahs?

It is not permissible to combine two intended prayers with a single intention, such as the Sunnah of Isha' and Qiyam al-Layl (night vigil prayer), because both are prayers intended for their own sake. This is indicated by the fact that the night prayer cannot be obtained through other prayers, and scholars have not mentioned it among the unintended prayers, and it is made up for those who habitually perform it. As for the prayer of need (Salat al-Hajah), it is not intended for its own sake, so it is permissible to perform it with the Sunnah of Isha' with a single intention.