I can't find any rules for REACTIONS.
It appears that it is an ACTION word (since it's in all caps), but you can only use ACTION words on your turn (per the rules), which would mean you can never do a reaction.
Can you do the same reaction multiples times in a round/turn? Can you use more than one reaction in a turn/round? Can you use 2 different reactions due to the same trigger?
Haunt 0 has instructions for how Reactions work.
In general, reactions trigger every time the condition is met, they aren't actions, and if 2 reactions have the same trigger, they would both trigger.
Do you have an example of 2 different reactions having the same trigger?