Barb,
Can you PM me and let me know how you're getting that high rate with RBC? I've looked over the rate book and can't see it at all. Also as far as I can tell there is no family package rate that includes cancellation insurance - the only mention of "family" that I can find is the medical-only plan.
As for why you're being told to sell RBC, if you work through an agency then most agencies have agreements with the various vendors. I know with RBC if you sign up for an exclusive with them then you get higher commission rates. The agency I was at last did this - they were allowed to sell a small amount of non-RBC insurance but not much. It was very restricting.
I sell Travelguard, and haven't had a problem with it yet. For your group, assuming everyone in the party is under 60 and the trip is for a week, then the insurance would come to about $200 with TravelGuard. TravelGuard also has a 24/7 help desk for the clients that they can call if they need to make a claim or need assistance.
One thing to be wary of with some of the "smaller" and lesser-used insurance companies is whether or not clients have to pay for expenses out of pocket first, and then get reimbursed. Not too much of a big deal when you're talking things like meals and hotel for trip interruption, but can be a very big deal when you're talking medical expenses.