Hi Cassius,
Thank you for including me on the thread.
My technical knowledge is perhaps not high enough for me to really chip in, but I like Kalosyni's idea of compiling email addresses for everyone who would like to be included in the emergency network, simply because everyone could easily take part without having to learn another platform and would be something everyone would have access to. I do have Signal on my cell phone, as many people do, and I think that would be a relatively practical option, too.
Proton Mail offers free encrypted email accounts that I would think would be accessible to everyone, so that could be an option, too.