[Al Skierkiewicz]

Frank is correct on this rule. The solenoid module has limited current capability as is referenced in R42. However, this follows the table...
*Multiple low-load, pneumatic solenoid valves, electric solenoids or CUSTOM CIRCUITS may be connected to a single relay module. This would allow one (1) relay module to drive multiple pneumatic actions or multiple CUSTOM CIRCUITS. No other electrical load can be connected to a relay module used in this manner.
The diode shown in your diagram would really not perform as you want. The Spike can be used such that it feeds two solenoid branches with a single device. The outputs independently switch to +12 volts which may help your design. Spikes cannot be used for 24 volt solenoids.