ANSWER:

You should fear Allah and treat them with respect and obedience while being dutiful. 

Favoring your sister over you is sinful and Allah will hold them accountable for that. However, disobeying them and displeasing them is a major sin that you will be held accountable for no matter what your excuse is.

Stop being jealous and move on with your life and be grateful for whatever Allah has given you and you will find peace in being content.

QUESTION: Sheikh, i love my parents soo much,And they love me too.but they tend to give more attention to my sister like buying her things that i don’t have,and sending her to summer classes while they didn’t care abt what i wanted to do.they tell that they will do this n that if i do something and after i do,they just don’t care.it’s frustrating and i disobey sometimes,advise me,i am afraid of losing janna