i have 2 pumps with 1 res setup
The only situation where this setup will work is when there are too many blocks for 1 pump alone. With 2 pumps, there will be two loops so that each pumps can handle a smaller number of blocks, both the loops will dump liquid into the same res and get its liquid from the same res too.
Also, one benefit with 2 loops sharing one res/fluid when running different size radiators is that you wont have to worry about splitting the load/blocks between the different radiators. Since the same fluid will be flowing through all the blocks and radiators at a some point in time, you get the benefit of all the blocks benefiting from all the rads.
the top tubing is my fill port
the left-top is the "in" for the blue loop (3/8 ID)
the left-mid is the "in" for the green loop (3/8 ID)
the left-bottom is the "out" for both loops (1/2 ID) this one get split into the two 3/8 ID feeding each loops