Becoming a Christian is a huge decision to make. Shoot, it took me how many years to make it?? ha ha. Once you make this decision, it's important to realize that there are certain things that will start to change, namely YOU! :) Those who know you best will still remember the "old" you and resist. Here's some interesting thoughts on the matter.
First and foremost, you need to know that some of those who are closest to you will resist this growing up in Christ. When you read Luke 4:16-31 you quickly realize that even Christ had this problem in His hometown of Nazareth (See Matt 13:54-57). They wanted to know why He could teach with such authority when He was "just a carpenter's son." The people closest to you will potentially resent that you don't party with them or talk/behave in the same way (See 1 Pet 4:3-4).
You can try to change their perception of you by explaining "that was then," or explaining that you messed up in the past...own it (Prov 28:13). Once you do that, explain to them that "this is now" and you are changing who you are. Tell them that you are a Christian and want to be the salt of the earth and you want to shine the Light of the world (Matt 5:13-16). To do this we have to be willing to speak God's truth regardless. It becomes so easy to cop out with those who share our DNA and walked in our social circles. Just remember that it is very selfish to not care about their eternity. BUT!!! We must do this out of love and concern for the other person. AND!! We must live out the truth as well.
In life (and in poker) we must learn when to hold 'em and when to fold 'em. Jesus had to make this decision, too, while in His hometown. If you read Matt 4:12-13, you'll read that He left Nazareth and settled down in Capernaum. So, if what you're holding, God's Truth, isn't going to get the job done, fold 'em. We must not waste God's precious truth on those who will disrespect or attack it (Matt 7:6) Kindly and lovingly tell them that you will not allow them to disrespect your Dad. If they don't stop, you may have to sever the relationship, leaving a door open with them to come back and hear the truth. Remember Matt 10:34-39...it happens.
I want to thank my church, The Cool Church, for this teaching. It is painful when your own family reacts badly to your becoming a Christian. I know for me, I had to distance myself for a while until I was a more mature Christian...not because they attacked God so much as it was for me, because I couldn't yet resist the DNA and/or social circle temptations. I've learned how to handle it better; definitely not perfect at it yet, either. :)