Please, give us additional details about your shared disks, like if you are using shared VMDK or RDM... keep in mind that in both cases you will need a dedicated SCSI controller and depending of the type of shared disk you may need to run both VMs on the same ESXi host.
The following guide show the detailed steps to configure the cluster, please double check if you are not missing any steps and/or requirements: https://docs.vmware.com/en/VMware-vSphere/6.5/vsphere-esxi-vcenter-server-651-setup-mscs.pdf