These are the online options if you start a booking on the DB site for 3 adults traveling together. I do expect the computer to keep you as close together as possible, and I also think there's only one car for the deluxe sleepers. If you want a different combo, you'd have to do it by phone or by booking the two parties separately.
three persons in Economy T3 compartment breakfast incl. 387,00 EUR 464,70 EUR
three persons in Economy Double compartment breakfast incl. 447,00 EUR 524,70 EUR
three persons in one Economy Double + 1 Economy Single compa 487,00 EUR 565,70 EUR
three persons in three Economy Single comp. Breakfast incl. 567,00 EUR 647,70 EUR
three persons in Deluxe T3 compartment breakfast incl. 507,00 EUR* 657,90 EUR*
three persons in Deluxe Double compartment breakfast incl. 567,00 EUR* 717,90 EUR*
three persons in three Deluxe Single comp. Breakfast incl. 687,00 EUR* 840,90 EUR*