My dad drinks beer a lot. I mean like 6 cans a night. He effects us all! What should I do?

Keep out of his way.

Seriously what CAN you do that won't degenerate into a fight?
You can only get him help if HE wants it...

Saying that 6 cans of beer a night isn't a huge habit.
If it was through out the day, or spirits then that would be much more serious..

While it is a bit, 6 cans is really not "a lot" of beer, I know many that do 12 and more in a evening.

But there is nothing you or any one can do, he has to decide he wants to quit on his onw