cancel or no show?

Heedtheadvice

Two things I would do considering that it is (?) a group booking is to find out in advance what the situation is regarding one of the group travelling later (if that is at all possible) or one group member having to cancel altogether (depending upon if that person can travel later or not for whatever reason or is not fit to travel at all) from the company you bought the holiday from. It could potentially affect the conditions surrounding the group booking?
Secondly find out the contact for the airline, phone number or perhaps an on airport representative so that if your group member cannot travel (or travels later) you can tell them prior to departure, even if that is on the day.
At least then you will know of anything that affects your booking (thinking along the lines of something similar to single supplement, or minimum group booking numbers etc.) and will be armed with contact info for when you potentially need it.

Are you sure that the declared pre-existing conditions are not covered by the travel insurance? I know some policies do not cover but also some do. It should not a problem to get in touch with them in advance just to clarify and confirm and you will then know exactly where you stand. Some policies provide cover if a party member, relative or close associate affects your holiday arrangements. Asking should not have any negative connotations and the group members are possibly on different policies?
....mmmm that's a third thing.....

You might get some more useful specific responses if you can say who the travel agent, holiday provider, airline and destination is,......but don't post your address and travel dates!!:T for what should be obvious reasons!
.......oops that's four things........

I know you have stated some of these things already but no harm to double check in advance, is there, purely for peace of mind?