We have a similar problem at school, for emergency closures etc, and have telephone "tree".
One person initiates a message by ringing a few people, who then each ring a few more and so on.
As long as you put the more "reliable" at the top of the tree, the system works well.
Obviously you would have to work out who contacts who, but in theory, each member should only have to send one PM.
You could even have a "lost comms" policy, whereby everyone responds to you acknowledging the message.
Animadvertistine, ubicumque stes, fumum recta in faciem ferri
(Ever noticed how wherever you stand, the smoke goes right into your face?)