Does anyone know if RSR has their own spanner wrench size or can I use the ones from BC to adjust the coilovers?

Spanner wrench are pretty much all the same. I have no experience with RS*R but I think you should be fine using one that were meant for different brand. All the years I've messed with cars I just grab a random spanner wrench from my tool box from a set of don't remember from which coilovers and start adjusting without worries. Even if it's the wrong diameter size wrench, still should be able to get by with it