I want it to be small, thats all, router is too big.
How far away is Arduino "A" from computer/controller "B" from computer/controller "C"?
What is the RF interference environment? How likely is RF interference?
How fast must it work? Can you overcome temporary interference by sending the command several times?
Is there a need for status read-back?
How does computer/controller "B" know that Arduino "A" got the message?
How does computer/controller "C" know what Arduino "A" or computer/controller "B" is doing?
How important is this "electricity control"? Is this a Life/Safety issue? is it secret so you can't tell us?
Are Arduino "A" and computer/controller "B" and computer/controller "C" utility mains powered or battery powered?
What exactly is the size requirement? We are going to get tired of the game if we keep suggesting things and you tell us "it is too big".