Can I use iMessage in Beeper if I share my Apple ID with someone else?
TL;DR
No, it's not recommended
It's not advisable to share your Apple ID with someone if you're using iMessage with Beeper - neither does Beeper support this.
Your Apple ID keeps track of all the aliases you use when sending/receiving messages, which is how Beeper differentiates between participants in a chat. Sharing your Apple ID (and, in turn, iMessage) with someone other than yourself can have unwanted effects on your experience when using iMessage with Beeper.
As per Apple’s recommendations, Apple IDs are meant to be unique to each user.
We can advise creating an Apple ID per user and grouping them under the same iCloud Family Sharing set up, if that is more manageable for your needs: https://www.apple.com/family-sharing/