My Cluster state is STABLE but Resource Group on both nodes is UNMANAGED.
This means that the cluster will not do anything even if the node where your application runs would crash. "UNMANAGED" means the RG is not running as part of the cluster at all.
To correct this stop the application, unmount its filesystems and varyoffvg its VGs. Then use either SMITty or the clmgr command to start the resource group on one of your nodes. This will mount the FSes again and start the appication, so from a users POV nothing has changed. From the clusters POV, though, the RG is now under observation by the cluster services and if the node fails somehow (crashes, loses network connectivity, whatever else) the RG will be taken over to the other node.