On a single loop, Parallel pumps are not going to provide any real benefit. Serial pumps will.
Also, you really need to separate the res outlets, to one for each pump. At max flow you could slow down the fluid to the pumps going through a single set of fittings.
If you were hoping to separately manage loop temps, you can't do that with a single res.
Suppose you placed both pumps in serial operation with one outlet from the res. THEN run your parallel loop with 2x 360 and one Heat Load on each side.
Same as what you have EXCEPT 2x pumps increase the flow and you have redundancy against one pump failing.
BTW - Wow! a Caselabs Magnum M8! You better put that in the will for your kids.
Build: msi C8r (Carbon8r)
Core i7-9700K, MSI Z390 GAMING PRO CARBON Mobo, AMD Radeon VII GPU, Corsair Vengeance RGB 32GB DDR4-3200 RAM, Phanteks Enthoo Pro M SE ATX Case.
XSPC RayStorm Pro CPU w/b, Bykski Radeon VII GPU w/b, EKWB 140 Revo D5 Pump & Rez.
Aquacomputer Aquaero 6 LT USB Fan-Controller, Vision Touch and 'High Flow' Sensor.
(2x) Hardware Labs Black Ice Nemesis 280GTS XFLOW radiators in full push/pull with 6x Deepcool RF 140mm & 2x Prolimatech 140mm Slim Fans.