ÖBB will let you enter 3 adults and 3 children, but won't sell the entire route. Trenitalia limits you to 5 passengers and doesn't appear to show discounted fares. Looks like the best bet is to call DB, or send in their Enquiry Form and they will get back to you with a quote.
Connecting in Munich would be easiest since the CNL originates there; you could board 20-30 minutes before departure and get settled in, as opposed to boarding at a downline station and making up the beds while the train is in motion.