Canbus, Opencan and ISO BUS
No, both are ISO 11898.  
No. ISOBUS is a derivative of J1939. But I do not own the documents of ISOBUS.
CANopen is unique above the data link layer, it basically eliminates the option to have multiple protocols on one bus. Most of them don't allow this actually. But ISOBUS and J1939 are compatible because they are designed to be.    
Since both use CAN bus physical and data link layer, you only need software and maybe a different connector type.  


If you are going to work with ISOBUS you should buy the standard!