Hey ozgoddess,
From what we understand, you're wanting to know if other trusted devices tied to the Apple ID you're trying to sign in with will be prompted with the two-factor prompt when you sign in with your Apple ID for iMessage. We'll help clarify.
It is possible that those other devices will see the prompt. However, this might vary. If the iPad you're signing in on is already a trusted device for that account, you can accept the sign in directly on the iPad.
For more info on two-factor authentication prompts, check this out: Two-factor authentication for Apple ID
We hope this helps. Cheers!