What are the stability issues you're facing? Data volume if used as a data storage domain should be a replica 3 volume as well.
Deploy the hosted-engine on the first VM (with the engine volume) froom the CLI, then log in Ovirt admin, enable gluster support, install *and deploy* from the GUI host2 and host3 (where the engine bricks are) and then install host4 without deploying. This should get you the 4 hosts online, but the engine will run only on the first 3Right. You can add the 4th node to the cluster, but not have any bricks on this volume in which case VMs will be run on this node but will access data from the other 3 nodes.