Use Model-View-Controller framework. It's been said, yes. And, have at least one engineer for each part.
Model: Your DBA should write the Model code. No should else should be allowed to write SQL statements.
View: The one with the best knowledge of CSS and Javascript should do the view part. He/she should write the least PHP code, he is the one using PHP variables.
Controller: She's the real PHP coder, and also back-end server engineer, hopefully, with or without using other script languages.
