will Pro Mariner Pro Sport 20 charge multiple batteries?

I will make this as simple as possible.

My current set up:

-(3) Kinetik 2400's - dedicated stereo batteries - run in parallel
-(2) Interstate cranking/starting batteries
-(1) Pro Mariner Pro Sport 20 - dual bank charger

Total = 5 batteries and 1 dual bank charger

My question: Can my Pro Sport 20 charge my (3) Kinetik 2400's as Bank 1 and my (2) Interstates as Bank 2?

Ian @ Pro Mariner says it can't be done and that EACH battery needs its own bank. He basically said that Im not getting a full charge on all my batteries even though the Pro Sport 20 says it's READY/CHARGED. He suggested that I move the Pro Sport 20 (2 bank) on my two Interstates and add a Pro Sport 20 PLUS (3 bank) on to my three Kinetik 2400's. This all makes sense logically.

The curve ball:

I hammered the Kinetiks over the weekend down in the 11's and actually killed one of the Interstates. The boat has been plugged in since Saturday night. I just tested each Kinetik 2400 individually as well as in parallel and the voltage meter read 13 volts both times. My Interstates also read 13 volts as well. If a dual bank battery charge can't charge all these batteries then why am i getting these voltage readings?

I realize that the best thing to do is throw a 3 bank on the Kinetiks 2400's and throw the 2 bank on the Interstates - it surely will charge quicker. Im sure over time the Pro Sport 20 dual bank will crap out due to being over loaded with 5 batteries? But if they say it CANT be done then why am i able to charge the batteries back up?

Thanks in advance!