Combine photos from multiple people's iPhones into a single location?
Use Google Photos. This being a fairly new app, it did not exist at the time this question was asked. 

Google photos is a new (free!) service that allows you to upload all your photos to Google Drive, automatically. You can also share all your photos with anybody you want, using the new Share Your Library feature. 

You can download the app from the App Store, or access them on your computer. There's also a desktop uploader in case you want to upload photos on your computer automatically.

The best part about this app is that it allows you to delete all the photos you uploaded from your phone, freeing up storage space on your phone. Your photos will still be available through the Google Photos app.