assalaamu alaikum
My maternal grandfather usually scolds,mocks my mother because she sleeps during daytime 2hour after fajr till dhuhr but my mom regularly prays 5times a day
On other hand, he does not even advice,preach to my mother's other sisters who perform their fard prayers rarely,dont fast during ramadan,dont try reading&understanding Qur'an etc.
Is my grandfather behaving in the right way?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If what you mentioned about your grandfather is true, then he is wrong for mocking your mother and blaming her for sleeping during the day, while failing to fulfill his obligation to advise and guide his daughters, and to enjoin them to do good and forbid them from doing evil, as he is religiously obligated to do so. Allaah Says (what means): {O you who have believed, protect yourselves and your families from a Fire whose fuel is people and stones.}[Quran 66:6]

Ibn ‘Umar narrated that the Prophet said: “Every one of you is a guardian and is responsible for the people under his guardianship: the Imaam (Muslim ruler) is a guardian and is responsible for the people under his guardianship, a man is a guardian in his house and is responsible for the people under his guardianship.” [Al-Bukhari and Muslim]

Indeed, both abandoning the prayer and neglecting the fasting of the month of Ramadan are great sins as we clarified in Fataawa 85264 and 83368.

As regards abandoning the Quran completely and abandoning pondering over it, then this is included in the matters that Allaah dispraised as He Says (what means): {And the Messenger has said, “O my Lord, indeed my people have taken this Quran  as [a thing] abandoned.}[Quran 25:30]

Hence, your grandfather should urge his daughters to recite the Quran and to ponder over its meaning.

Allaah Knows best.