I am not sure if you are journaling on a computer or in pen on papper but either
way you might consider writting in the "third person" as a story.
Give your self a pen name, that way if family comes accross it you can always say it is about a friends' life or a story, fiction.
You can give the real characters in your life different names.
Be creative.
There are journals with locks at the bookstore, post office has boxes, in you home if you are on the computer buy a blank disk and write there save to disk, then delete file, and you should be fine.
I would also encourage talking to parents in a soft, calm, non defient way. Remember to let a person talk and listen, then reply. Dont react with an emotional outburst. If this does not work then maybe therapy would be good for you.
Hope this helps!
H.