To control both pumps in Aquasuite you need to have both of them connected via the aquabus, not just one of them.

Two pumps of the same type together will have a different effect whether they are connected in series or in parallel. In series will give you double the head of just one pump, useful for overcoming the loss of head as coolant moves through a system. Two pumps in parallel will increase your flow rate for the same head, useful when one pump alone cannot cope with the volume of flow.

Pressure is not created by the pump, only flow is.

Pressure is the resistance to the pump flow. Anything that slows down the coolant passing through the pump is creating pressure, so things like the tubing, waterblocks etc, even the pump casing itself.

None of this is really very useful for such small systems like those in our computers. The pumps we have available for that purpose are more than sufficient for most situations. I think that one of the aquastream XT pumps should be enough for your loop.

Hope this helps