Syncing multiple iPhones to a single computer can put your media libraries, backups and devices settings into disarray, especially if you share the computer with other Apple device users. You can avoid these iPhone management issues by using unique Apple ID accounts, creating separate iTunes libraries, using separate playlists and syncing with iTunes across different PC user accounts.

Authorize a Computer With a New Apple ID

Launch iTunes on your computer and open the "Store" menu. Click on "Authorize This Computer" and type in the username and password attached to an iPhone. Repeat this process for each subsequent iPhone user who wants to sync her device with iTunes on this computer. Authorizing your computer with these new Apple ID accounts allows these users to manage their media and app purchases in iTunes.

Create a Separate iTunes Library

While multiple Apple IDs keep your purchases separate, other user media can still get mixed up, causing unpredictable syncing behaviors. Creating a new iTunes library for each iPhone user can reduce instances of mixed media files and cross-synced data. Hold down the "Shift" key and launch iTunes. Select "Create Library" and give the new library a custom name. Open the "Edit" menu, choose "Preferences" and click "Advanced." Uncheck "Copy Files to iTunes Media Folder." Add media to your new library by dragging and dropping audio and video files into iTunes. To switch to other libraries, close iTunes, hold down the "Shift" key and launch iTunes again. Select "Switch Library" and click on the user library you want to open.

Syncing With Separate Playlists

Instead of creating separate iTunes libraries, users can keep their device media separate with playlists. Launch iTunes and create a new playlist with media attached to your unique Apple ID. Plug your iPhone into your computer with a USB cable. Choose your iPhone from the Device toolbar, click on the "Music" tab and choose "Sync Music." Click "Selected Playlists, Artists, Albums and Genres." Check your playlist and click "Apply" to sync your media with your iPhone.

Create a New Computer User

Sometimes it's not enough to separate your media with different Apple IDs, playlists and libraries in iTunes. Your contacts and calendars can get mixed up with other iPhone users syncing to the same computer if you do not have separate computer user accounts. Open the "Settings" menu on your PC and choose "Change PC Settings." Click on "Accounts" and choose "Other Accounts." Click "Add Account" and then "Local Account." Create a username and password for this new PC account. Click "Finish" and sign in with the new credentials. Launch iTunes on your new PC account, authorize your Apple ID and move your media into the iTunes library. Move your contacts and calendars onto this new PC account. The next time you sync your iPhone, it only uses data stored on this user account.