iPhone A - Apple ID A
Iphone B - Apple ID B
When connect to iTunes to same desktop, loggin by Apple ID A, iPhone A can sync, backup (local backup, not iCloud), and restore from backup, iPhone B cannot.
When connect to iTunes to same desktop loggin by Apple ID B, iPhone B can sync, backup (local backup, not iCloud), and restore from backup, iPhone A cannot.
- You can attach two iPhones to your desktop at the sametime and iTunes will still sync both concurrently. (So it doesn't matter)
- You can login to either AppleID_A or AppleID_B with the two iPhones connected CONCURRENTLY. [So it does not matter which AppleID you log into, no one says you cannot]
Backup is fine - Backup is INDEPENDENT of AppleID.
The only issue you would have is the content, like Apps/Music/Movies purchased under different users.
Because iTunes will only hold one of the App, they do not hold duplicates.
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Personally, I would not recommend you to sync and transfer purchases by different users in the same iTunes library.
I would recommend that you should use different iTunes libraries for different iPhones.
Let me give you a situation:
Today, you install Whatsapp in iPhoneA, and your wife install Viber in iPhoneB.
You sync it, your iTunes will have Whatsapp_AppleID_A and Viber_AppleID_B.
Tomorrow, you install Viber in iPhoneA, and your wife install Whatsapp in iPhoneB.
You sync it, No app is sync-ed.
[
Overview:
iTunes(Computer) have Whatsapp_AppleID_A and Viber_AppleID_B
iPhoneA have two apps: Whatsapp_AppleID_A and Viber_AppleID_A
iPhoneB have two apps: Whatsapp_AppleID_B and Viber_AppleID_B
]
You don't install anymore app, and then one week later, you both get a new iPhone, and you sync it with your iTunes.
You restore from backup.
Now this is what happen.
New_iPhoneA will have two Apps. Whatsapp_AppleID_A and Viber_AppleID_B.
New_iPhoneB will have two Apps. Whatsapp_AppleID_A and Viber_AppleID_B.
Now you have a situation here.
If Whatsapp and Viber comes up with a new update,
- you will have to login to wife AppleID to update Viber.
- your wife will have to login to your AppleID to update Whatsapp.
> So to make things simple, either
- use 1 AppleID for all or
- use separate iTunes library for separate AppleID
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Another scenario:
iPhone A - Apple ID A
iPhone B - Apple ID A
When connect to iTunes to same desktop, loggin by Apple ID A, each will sync to and have a set of local backup, and can restore from their own backup.
Backup is INDEPENDENT of AppleID. This means it does not matter which Apple ID you log into. If you want, you can even login to your friend's Apple ID and you can still Backup.
Also:
iPhone A - Apple ID A to login App Store, thumb print A to install App
iPhone B - Apple ID A to login App Store. Can we use thumb print of B to install App? Let's say, it is using thumb print B to unlock phone.
Sorry for the long questions.
Thumbprint is INDEPENDENT of AppleID. Thumbprint data is only kept/embedded in the same iPhone you configured.
Therefore, Yes, you can use Thumbprint of B to install App on iPhoneB using AppleID_A.
This is because the ThumbprintB is only kept in iPhoneB and since you saved AppleID_A into iPhoneB. ThumbprintB can be used to access AppleID_A.
I hope that clarifies your questions.