Don't tell your parents that you don't believe in God etc. If you really need to talk to them about it, tell them that you have doubts and that you are not sure what to believe. If you make such a drastic declaration you will come across as an "Apostate"...
I have talked to my relatives about TTATT for some years now and the "Apostate alarm" still goes of if I suggest that God doesn't exist...
So be gentle with them ;)