I’m not really sure MC_Spawn is needed. Just the call on the server should do the trick - ROS_Spawn to spawn the actor. Just make sure the actors you spawn are replicated and that you call the server function from a BP that is owned by the client. (i.e. from the character you control)
P.S.
@Nightwolf suggestion might also work but you should relay on replication instead of multicast events whenever possible.