When the first unit gets out of your way, draw two lines straight forward from the outer edges of your charging unit. If those contact another enemy unit, you get to declare the new charge. Stand & Shoot is resolved just like normal. The defenders fire before the chargers move, or as soon as the chargers come into range of all the defenders if they started outside.
Also, be sure to read the errata for Enemy in the Way in the
FAQ:
http://us.games-workshop.com/errata/assets/warhammer_v7_faq.pdf