Did Cain have brothers and sisters?

Question: In Genesis 4:14 why did Cain say anyone can kill me on sight if there were only his parents alive at the same time?

Answer: Genesis 5:4 tells us that during Adam's long lifetime of 930 years (800 years after the birth of Seth), he had other sons and daughters. Since he and Eve had been ordered to produce a large family in order to populate the earth (Gen 1:28), it is reasonable to assume that they continued to have children for a long period of time, under the then ideal conditions for longevity (Encyclopedia of Bible difficulties; p.77).

The Douay Rheims Bible says regarding Cain: "His guilty conscience made him fear his own brothers and nephews; of whom by this time, there might be a good number upon the earth; which has now endured near one hundred and thirty years; as may be gathered from Genesis 5:3, compared with Genesis 4:25.

Another footnote in the Douay Rheims Bible explains Genesis 4:17 which refers to Cain's wife. The footnote says: "She was a daughter of Adam, and Cain's own sister; God dispensing with such marriages in the beginning of the world, as mankind could not otherwise be propagated."

God started humanity with one couple; thus the whole human race are brothers and sisters. It was not till Leviticus 20:17 where brother sister marriage is forbidden for the 1st time in the Bible. But for Cain and Seth and all the other unmentioned sons of Adam and Eve, they must have chosen their sisters as wives (ibid).

Question: Is it wrong for me to pray to not have human emotions such as hatred, anger and jealousy?

Answer: Emotions such as hatred & anger are normal, however we must master them and not be mastered by them. They are mastered by having a well formed moral conscience and living in a state of grace. Jealousy is more than likely a venial sin because at the very least you lack charity for another person, however the motive has to be scrutinized because it may be entirely rational (read: https://www.catholic.com/encyclopedia/jealousy).