As I understand you have a shared vmdk assigned to virtual machines and this vmdk resides on a shared LUN presented to all hosts. and you have a cluster configuration between virtual machines using same vmdk.
for that there is a way to share the ISCSI controller and the disk from virtual machine settings. the following document should help you (it is related to microsoft cluster on top of vmware but in the vmware configuration part will help you): https://docs.vmware.com/en/VMware-vSphere/6.5/vsphere-esxi-vcenter-server-651-setup-mscs.pdf
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This is a difficult question to answer here.
As it appears you are using the free version of ESXi then there is no support from VMware (apart from what you might get in the community). Given the impressive list of hardware you have it makes me wonder why you don't look at either ROBO or VMware Essentials so that you can run a vCenter and all the lovely goodness that comes with that
It could work but personally too much risk for me with this setup. Could be done with appropriate checks and balances in place but not worth the risk.