Wa alaykum assalamu warahmatullah,

In the Name of Allah, the All-Merciful, the Mercy-Giving

All praise is due to Allah alone; peace and blessings be upon Our Prophet Muhammad.

This is a very shocking question indeed. May Allah help you and your sister overcome this hard test.

Regarding your sister, she needs intensive care and support. She needs to boost her faith and trust in her Lord so that she should exclude the evil notion of committing suicide. She needs to come closer to Allah through various acts of worship (praying, fasting, reading the Quran, etc) and through earnest supplication to Him to relieve her distress and help her overcome the pains and feelings she suffers. Attending religious classes and associating with pious friends will also be helpful. It will be much better if you can take her to make `Umrah.

As for your father, if he has certainly done that, he then has committed very enormous and heinous sin. I can understand the negative feelings that you and your family have towards him. But still he is your father. No sin is greater than associating other gods with Allah SWT; nevertheless, we read in the Quran “But if ever they strive in order to compel you to associate gods with Me- [or command you to anything] about which you have no [sure] knowledge [from God]- then do not obey them. Yet [still] keep company with both of them in this world, in accordance with what is right. But follow the path of one who turns to Me in penitence.”  (Luqman 31:15) So, anyway, you have to be dutiful to him and try to be kind with him as possible as you can.

Your father needs to repent sincerely to Allah SWT. If he regrets what he did, you and your family need to forgive him and help him repent sincerely to Allah SWT.

May Allah keep you steadfast on His religion.

Allah knows best.