I'd consider doing the upgrade in 2 parts: the Windows upgrade first followed by the Connection Servers in that order.
Obviously, i would de-risk the Wins upgrade on a dev rig or Workstation lab to see if the upgrade is smooth - i take it none of these Wins Servers have any roles included? From my limited experience of Wins there will always be a hiccup with the in place upgrade. Once satisfied that the Wins upgrade is known/stable I would then proceed to do all other Operationg Systems before doing an Horizon Connection upgrade, which should be relative straightforward. Check your View AGents on the VM desktops are compatible with the proposed Connection Server.
