Pshew!! 30 - 35 is a quite a large number to take care of.
In 2001 I walked the Coast to Coast in England with a group of 10 women. We took it in turns to be at the front and after your turn, you went to the back of the group.
The person in front and at the back each carried a loud whistle. If a car was heading towards us, the leader would blow the whistle and any stragglers walking in two's or three's would hop back into line. Same at the back - if a car came from behind the group, the last person blew their whistle and we all formed a single file.
We agreed before hand that if anyone was injured, ill or exhausted, that they would get a bus or taxi ahead to our overnight stop and wait for everyone else to catch up, rather than expect someone in the group to interrupt their walk to be with them.
This was not difficult as we booked all rooms ahead of time because some villages are so small (Keld comes to mind) that they might not have been able to accommodate us at short notice. Perhaps you should consider doing this too? July can be a busy month on the camino.
Have a great walk!