DON'T DO THIS - Signal is not as private and secure as you think
  • It leaks metadata
  • It requires a GPS tracker (a phone number)
  • You cannot run on your own servers
  • It has unavoidable google services (eg captcha)
  • The builds are not reproducable
  • It contains binary blobs (not completely open source)
You'd be better off taking the time to get them onto a properly secure and private messenger, such as:
  • Simplex Chat
  • Session
  • Briar
In any case, the solution here is simple. Just delete all those spyware apps (Signal, Telegram, Whatsapp, Viber) and communicate ONLY on secure apps like the ones above. Or email.