All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The jurists stated that a traveler should perform the prayer without shortening it, whether he is led in prayer by a resident or he performs the prayer individually, if any of the following cases happen:
· He started the prayer intending to complete the prayer.
Consequently, if the situation is as you mentioned regarding the prayer in which you were led by a resident, then you should have completed the prayer 4 Rak’ahs and not concluded it after praying 2 Rak’ahs only. This also applies to your sister as she started the prayer while intending to complete it and not shorten it; she also should have completed the prayer. Therefore, you are obliged to make up for that prayer.
As regards not combining Thuhr and ‘Asr prayers at the starting time of Thuhr when you travelled to Madeenah, then your prayer is valid and you are not sinful for not combining the prayers. Combining the prayers during the travel is permission granted to the traveler and not an obligation; for more benefit in this regard, please refer to Fatwa 88710 and 88402.
Allaah Knows best.