Is it sufficient to perform one Hajj on behalf of both parents in one season or should I perform Hajj separately for each of them if I want to be dutiful to both of them?

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is not valid to assume Ihraam to perform Hajj on behalf of two people in one season. Consequently, you cannot perform Hajj on behalf of both your parents in one season. You must dedicate this Hajj for one of them and then perform another Hajj for the other. Please note that you can perform Hajj for yourself and then gift the reward of your Hajj to both your parents, because this is permissible, and the reward will reach both of them, Allaah Willing. However, it does not serve as performing Hajj on their behalf.