How does it work when assaulting a squad of tanks? I have a friend that uses three Leman Russ tanks in a squad. I would like to assault them using my 9 man Vanguard Veteran squad equipped with melta bombs. I should have 9 attacks on rear armor at strength 8 with 2D6 armor penetration.

Do I only assault the tanks I am in base contact with?
If so does my opponent still spread the penetrations over all three?
Do I have to put 3 attacks on each tank and then roll to hit?

I'm so confused.