are we allowed to power multiple solenoids off of one spike relay? if yes, up to how many?
Please be more specific in your question.
If you are referring to the Pneumatic solenoids provided in the OCCRA kit of parts the answer is yes as you are limited to the quanity in the kit and no more of any type or any other source.
Note: In reviewing the official parts list given to you, there are only 2 Solenoids in the kit a 5/2 single and a 5/2 double.