How do you use datasheets and that information to determine how many devices supported on a circuit?
It depends on if source is AC or DC for load ratings. Shall see when specs arrive.

I would suggest you choose modules with Temporal loads rated for &lt;=18mA which exist,  then the 150mA std output rating can fan out to 8 units.

Update 
Indeed these do not drive more than one external units. Some have a 1pps Strobe flash with even more load power depending on brightness setting.

I suggest you call/email supplier for interface clarification and alternatives for cost-benefits to suit the requirements.

www.systemsensor.ca/literature/CIM2B.pdf  These are 18mA