My father has hardly ever prayed more than a total of 2 months in his 75 year life span, and I’m sure my mom who prays every day has missed some prayers that she is yet to make up, my two older brothers don’t pray either.

Tthe question revolves around the death of my parents, when their time comes, I’m under the understanding that it is obligatory upon the eldest son to make up the prayers of the parents (my dad is sunni and my mom is shia, im personally shia but my oldest brother follows sunni ideology when he does pray), either by doing them himself or by hiring someone to make them up, but assuming both my brothers think that this is a far fetched idea, would I be able to shoulder that responsibility (paying for their prayers to be made up) and if I perform hajj for my father, or for my mother, or for both, does it still count towards me as well or does each hajj need to be performed on separate occasions in order that it reaches them?

Also a final question, which are the best acts of sadaqa jareyeh that can be done for parents and family members?

Yes you can pray on behalf of your parents even though you are not the oldest. You can hire someone to pray as well if you choose to do so.

For a Wajib hajj, you can only perform it on behalf of one person. Also in order for you to perform the hajj you need to have performed the hajj on behalf of yourself in a previous year. You can give money to someone to do the niyaba as well.

There are many acts of sadaqa, one can recite Quran, give charity, do righteous deeds and pray for parents. These are all good.