Swap whole content of two iPhones

I would suggest you consider using the BackUp process within iTunes to help with this problem, BackUp each device and Archive each with a unique name (if you don’t they may replace each other), then Restore each device with the “others” BackUp.

Due to some differences between the two devices I would consider some final minor manual setup will be required but the major legwork should have already been completed, but I’m not sure how the content in iCloud will end up because it’s usually linked to the Apple ID and if you use that ID on both devices then I would think they will end up with the same synced iCloud info.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

The above is just my thoughts on how you may achieve the “swap” but I’ve never put it into practice, may be someone else has.

No offence, just for reference. Re-download varies from country & region, refer the link below...

https://support.apple.com/en-in/HT203768

About your apps, music, movies, and TV shows

The content that you buy from iTunes, the App Store, and Apple Books lives in iCloud. But iCloud Backup includes only information about that content, not the content itself. After you restore from iCloud Backup, your purchased content automatically downloads again from the iTunes Store, App Store, or Books Store. Availability of iTunes re-downloads varies by country or region. Previous purchases might be unavailable when they've been refunded or aren't available in the store anymore. Some previously purchased movies might not be available for re-download from iTunes.

For some third-party apps, you might need to download data from the app provider again.

If you use iTunes Match (where available), you can use it to download previously matched or uploaded songs, albums, or playlists to your device. To recover content that wasn't purchased from the iTunes Store or isn't available through iTunes Match, sync your device using iTunes on a computer that has your content.

To recover content purchased with a different Apple ID, sign in with the Apple ID associated with that purchase.

There is no way that you can transfer apps from one device to another. However you can download apps which are available on one and not on the other.

Since you are using same Apple ID it is quite simple for you. Watch the GIF below

Thank you, I realise Apps are redownloaded but that process is “Automatic” and triggered by the Restore process itself (if Restoring a devices BackUp), it was the content that is “synced” via iCloud that I was uncertain about, ie Contacts, Calendar, Safari, Notes ect, they are usually linked to an Apple ID, if both devices use the same ID then I would think the same content would sync back to both devices.

No offence taken, and must admit did not consider the possibility that some Apps may no longer be available for redownload.

I suppose the point is when trying to undertake a process such as swapping content between two devices there is always a risk something may be lost, so it would be wise to make alternative backup arrangements for that important content, be it old apps, pics or music.

back them up to a computer and restore then with each others backup

If you restore from backup you need to download all apps once again. Only the links and data of apps are restored. App themselves have to be downloaded again from App store.

If you restore from backup you need to download all apps once again. Only the links and data of apps are restored. App themselves have to be downloaded again from App store.