I think, he is youngest in the family. So the love he got is surplus, & he is spoiled.
Now this is duty of your father to make him understand, how to behave.
For some days all of you change the attitude towards him little bit.
If he cries let him cry for some time do not bother.
Do not fulfil his every command; stop giving too many things (toys, chocolate, drink & the things he likes.
But at night mom should tell her that everybody still love you, but you are not behaving good. I hope that he will be alright.