My experience is TPAC for these family groups and mission trips.

We found it best to go to a travel agent/consolidator who specialize in these route. Negotiate a fare from a gateway to your final destination on the same flight. Then a discount code with the same airline for the connections to the gateway.
The job of the group leader is easier if everyone fly over the water on the same flight as opposed to having to track everyone down in a different country.

It is nice for everyone to get FF points but dealing with multiple airline would increase the work involve and the cost as well. Some deeply discounted group fare does not earn FF points.

Since this is a family reunion, it is a good idea for the leader to fly in the same cabin as everyone else. On one mission trip I was given op-up by NW and I never heard the end of it.