Is it permissible to pray for mercy for deceased non-Muslims?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
Yes, it is permissible to pray for mercy upon them.
And Allah Almighty knows best.
Is it valid to share in the 'aqīqah by contributing a seventh share of a camel or cow?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
Yes, it is permissible. If a group of people jointly share in the slaughter of a camel or a cow on behalf of seven individuals, this is valid — regardless of whether all of them intend the 'aqīqah, or some intend the 'aqīqah, others the uḍḥiyyah, and others simply the purchase of meat. And Allah Almighty knows best.
Is it permissible for a husband to sell his wife`s jewelry if he was in a hard up?
A woman`s jewelry and dowry are her own property, and it is forbidden for the husband to take either without obtaining her approval. However, it is desirable for the wife to support her husband through considering her jewelry a sort of documented debt on him.
Is it permissible to give multiple mudds (portions) of fidyah to a single person?
Yes, it is permissible to give multiple mudd of fidyah to a single person, because each day of fasting is considered an independent act of worship.