First, on each phone, turn off FaceTime, iMessage & delete the iCloud account.
Back up each phone, then: Settings>General>Reset Erase All Content & Settings. Once complete, turn both phones off & swap sims. Turn each phone on & restore from the backups you made. Call your carrier & make sure they have the correct IMEI's for each account/phone.
For iTunes content, unlees you have both computers with you, one of you can just sync it back & the other can re-download or wait.
That's all you have to do.