Least sub-optimal configuration of flooded lead-acid cells with different capacities
There's only one sensible way to do this.


Make a 400Ah 12v battery with a series string of your six 2v 400Ah cells. 
Make two 225Ah 12v batteries, with two series strings each of six 2v 225Ah cells.  
Put all three 12v batteries in parallel to make one 850Ah battery.


Each series string has the same capacity cells in series (you must use the same capacity in series, or bad things happen (to the cells)). 

The three paralleled batteries have the same voltage (you must use the same voltage in parallel, or bad things happen (to the cells, and to you)). 

The capacity of all cells is used. You will be able to get the full capacity of all the batteries in parallel, 400+225+225 = 850.

You may have described this configuration in your OP, but it was tl;dr.