Why are you trying to turn a constant flow primary loop into a variable flow primary loop? Can your chillers even accomodate that much extra flow through them and still operate efficiently? My guess would be no without any other knowledge of the equipment.
Why not use a de-coupler loop between a constant flow primary loop and variable flow secondary loop to meet load?
i admit some confusion, believing that some data is missing here.
why would you need pressure boosting linked with water supply network in first place?
this looks to me as water tower network of water cooled chillers, where series connections serves to overcome large pressure losses, possibly risers are very long.
system is created without decoupling and that can work, being adjusted properly - main pumps sense demand from chiller pumps and match their flow to chiller demand as they are VFD-driven, and all chiller loops contain solenoid on-off valves.
all of that would make sense to me if we talk about water tower loop.
The booster pumps look fine to me, they just maintain a maximum make-up water pressure to the system when the city water supply does not have the necessary pressure.
The issue is with the control and sequencing of the chiller staging and the flow from the VFD pumps. The decoupler should help in that case.