Hydropneumatic tank for pressure surges
It is completely feasible to divide the volume into tanks. But you will have to make sure that you maintain identical pressure when filling for all three tanks and also have a hydraulic circuit between them that is as short and balanced as possible.
If there is a check valve with orifice on the tank to increase the pressure drop when filling, you will need to reproduce the system for each of the three tanks (the use of a check valve or bypass must be taken into account when sizing).
You may want to have your supplier recalculate the volume just to be sure. If the calculations were made 20 years ago, you may be able to optimize them by using newer simulation tools.
Yes, get the tank volume recalculated. There is a good chance that the recalculated volume will be lower.