Yes, I donn't think it's a particularly simple problem to solve, partly
because Word doesn't do "one to many" solutions out of the box and I don't
think just sorting your records into a particular sequence is going to be
enough.

There may be a simpler way to do this, but I would aim to create a new data
source that had columns

topname, listofnames

This would have one record for each participant, and a list of names
(probably separated by spaces) for all the other participants in their
group, e.g.

topname, listofnames
Don H., Mary K. Jane D. Peter M.  Kelly B.
Mary K.,Don H. Jane D. Peter M. Kelly B.
and so on

Then you would use that as the data source for your label merge, simply
putting { MERGEFIELD topname } (i.e. <<topname>>) at the top of each label
and <<listofnames>> below. There might be a word wrapping problem but let's
ignore that for now.

The question is how to create that list, and that really depends on what you
can use. It's actually not very difficult using Access, but...are you using
Access, and can you use it to create new tables and queries (preferably
using SQL) ? Or are you using Word and the facilities for data entry built
into MailMerge?

Peter Jamieson