Telegram is absolutely not vastly better than WhatsApp. Open Whisper Systems literally built the E2EE in WhatsApp. Its implementation of OTR predates signal.
Meanwhile, Telegram insists on rolling their own crypto and it’s closed source.
I think OP can and should try to get friends into Signal. But WhatsApp I’is almost certainly the answer to the OP. It offers well implemented proven off the record, E2EE communications, it’s widely adopted, cross platform. It’s miles better than SMS and Facebook or Instagram messenger or Snapchat. OP is looking for the best compromise, WhatsApp is it.
Keep your eye on the prize. Google and Mozilla aren’t even in the same area code of shit. Firefox is the obvious answer.