The VxRail upgrade will only upgrade 1 node at a time. Please refer tot he SolVe procedure for upgrading VxRail.
As for moving VM’s from one host to another during the upgrade, if the customer has an Enterprise license, then the VM’s will move automatically by DRS and vMotion. If the license is not Enterprise, and they do not have DRS/vMotion, then you will have to move the VM’s manually before the node can enter maintenance mode.
Hope this helps?