Kindly refer to the following link(s):
Reciting Surah Ya'seen over someone who is on his death bed
Reciting the Qur'an for a Dying Person
Reciting Surah Yasin & Praying a few Rakahs and giving it's reward to the deceased
What to do for someone who is on their death bed dying?
Any virtues of Surah Yasin? Reciting Surah Yasin after Fajr Surah Waqiya for poverty
What to recite when someone is sick