Swapping data between the two phones is a bit tricky. You can’t do that with iCloud. But is probably possible manually with iTunes.
You backup one device, then access the backup file directly from within folders > go to. Move that to a different location. Then backup the other device and restore your first device from this backup. Then swap that backup file with the one you’ve moved earlier and then restore the second phone from that backup.
I never had to do it but guessing that’s how it’s supposed to work.