1)-Wake up during the last part of night,pray 2 rakahs,and make dua.
2)-Enjoin goodness upon your Parents.Tell them to offer their prayers.
3)-To remove their stress,The best method there is,is Salah.It is proven from an authentic narration that the Prophet(Peace and Blessings be upon him),ordered Bilal,May Allah be pleased with him,to say the Adhan,when he himself was in stress,Peace and blessings be upon him.
4)-I have space to advice you.So here is something which is my personal experience.LISTEN QURAN RECITATIONS.IT EASES YOUR SOUL.ESPECIALLY YOUR PARENTS.MAKE THEM LISTEN TO QURAN RECITATIONS.
SHOW THEM TO YOUR SISTER AS WELL.
Trying it is better then not trying it right?
Also.
There is a narration in Saheeh Muslim,that a man who had committed 100 murders wanted to repent.So he went to a scholor and asked him if his sin was going to be forgiven at all.He had committed 100 unjust murders.
Do you know what he advised him?
He said your sin will be forgiven.But,
HE ADVISED HIM TO GO TO ANOTHER PLACE,BECAUSE THERE WERE RIGHTEOUS AND PIOUS PEOPLE LIVING THERE.
Meaning,he told him to keep good company.
In return for 100 murders!
So it is a must to change the company of your sister.
Go to another place.
And one last advice.
This may truly work.
GO FOR UMRAH.YOUR WHOLE FAMILY.
I HAVE SEEN GREATEST OF SINNERS RETURN BACK TO ALLAH IN THIS WAY.
DO IT NOW.
BUT,WHEN RAMADAN COMES,IT IS A MUST TO GO THERE.THE TARAWEEH AT MAKKAH,IS SOMETHING WHICH SOFTENS THE HEART.
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Here are a few Quran recitations.Beautiful Yes?
https://www.youtube.com/watch?v=Mn3Z-axJYXA
https://www.youtube.com/watch?v=BNXUqTkV6D8
https://www.youtube.com/watch?v=S2CQW92dLE4
https://www.youtube.com/watch?v=OQHp_o2TepY
https://www.youtube.com/watch?v=Z2xFv-aoArc
https://www.youtube.com/watch?v=YRK4HFG8os8