Two separate group chats with same group members?

I’ve seen this question several times, and the responses given don’t work. Please clarify.

I have a family group thread. I want to keep that for regular communication and create a separate group chat with the same people but use it for communicating about a one-time trip. Each time I try to create this new chat, I go to “compose” and add the contacts (all iPhone users), at which point, the existing family chat populates the screen. It will not create a NEW thread with the same people. How can I accomplish this, or what am I doing wrong?

I’m on iOS 18.2