Can I sync more than 1 iphone on an itunes account

Yes.

There is no device limit for the number of iDevices that can be synced with the same iTunes library and iTunes account on the same computer.

Absolutely...

http://www.apple.com/support/iphone/

Has your song been syncing his iPhone with a different iTunes account with iTunes on another computer?

oconnor44 wrote:

How do I do it without deleting my other sons iphone setttings/music?

Open itunes. Connect device. Select what you want to sync. Sync. Disconnect device.

Connect other device. Select what you want to sync. Sync. Disconnect device.

Connect other device. Select what you want to sync. Sync. Disconnect device.

and so on, for each device