Is Zakah due on the orphan`s money?
Yes, Zakah is due on the money of the orphan.
Is the son of the sister by breastfeeding considered a mahram in Islam, and is it permissible for a woman to go for Hajj with him?
Everything that is prohibited by lineage is also prohibited by breastfeeding. The son of the sister by breastfeeding is considered a mahram, just like the son of the sister by blood, and it is permissible for him to be her mahram for Hajj and Umrah. And Allah Knows Best.
What is the expiation for perjury?
Perjury is forbidden and one of the major sins that require turning to Allah in repentance, seeking His forgiveness, giving back rights to whom they belong, or seeking their forgiveness, and expiating for that oath.
Is buying and storing gold bars for profit permissible or prohibited?
Buying and storing gold bars for profit is permissible, and there is no harm in it. And Allah The Almighty Knows Best.