My wife and I have iPhones. We have separate Apple accounts on the phones. Can we share the same iCloud music and pictures?
Nope. The same account would need to be signed in on both devices.
You would need to both use the same iCloud account in order to share photos across Photo Stream. You can sync both devices with the same iTunes library to share music, while still using seperate Apple ID's within the iTunes store under the phone settings. (if you wish to continue using separate IDs for downloads)
iCloud does not sync music, so if the end result is to share all music downloads and photos the best advice I can give is to stop using one Apple ID and simply start using the same ID. There is no way to merge two IDs, only to both share the ID that contains more downloaded music and apps.
If you have a shared account for iTunes and individual accounts for Mail/Calendar/etc. it is possible to access iCloud music from several devices. Just make sure to log in to iTunes with the shared account on both iOS devices (and on the Mac).