Hello Danny,
in an HSRP group there is one Active router
one Standby router. All other routers are in the Listen State: they listen to HSRP messages that are sent to 224.0.0.2 all routers in subnets.
If one of Active or Standby fails the other routers move from Listen -> Speak and a new standby is elected.
There is no limit on the number of routers that can take part in a HSRP group a practical limit can be four.
If you have four routers and multiple clients I would suggest you to try to use GLBP to get load-balancing.
Hope to help
Giuseppe
