Hi and welcome.
If you have a 1.5" pipe as the header from the tank before your "Y" that will limit the max flow rate you can expect regardless of what pipes you have downstream of the "Y". You would need a 2" header at the tank to see any advantage fo extra pipes below the "Y" but it would be marginal. As the Head (and thus pressure at base) in the tanks drops, so too will the flow rate drop.
You could try using smaller diameter pipes to the people getting water and larger to the others who do not.
You could try and regulate that with a valve but I suspect people would tinker with the valve and mess up the balance. Far better to try and design your pipe runs so that flow rates equal out becuase of pipe diameters or lengths of total run.