Thanks for sharing your question with us, and welcome to the Automatic community! You're welcome to share the Automatic device between two users, however doing so requires a bit of work, so I'd recommend reading this FAQ, which addresses how multi-user works with Automatic. Most importantly: the adapter can only be aware of one account at a time. So if multiple users go on a trip together who all have accounts connected to that adapter, the adapter will connect to the first phone it “sees” and the trip will only appear in that person’s timeline.
I hope this helps answer your question, but if not, please let me know and I'd be happy to explain in more detail.