Using 2 Hyper-v servers (no AD) with replication to provide seamless swithover
Solution 1:
LIveMigration is required to avoid service interruption in you case. To enable LiveMigration and/or automatic failover you need domain joined WSFC (domain independent cluster doesn't support LiveMigration) and shared storage.
I can suggest the following cost-effective design:
1) Upgrade license to Windows Server Standard (you need it to license AD VM on each server)
2) Use VSAN to create a shared storage (Starwind vsan free for example)
3) Create domain joined Failover cluster
4) Deploy VMs
P.S. Technically you can do it with Hyper-V Server, but I am not sure, if the license allows it.
Solution 2:
You can use Hyper-V Replica and PowerShell script automated failover. See:
PoSh Hyper-V Replica Failover Automation
... just make sure you use some mechanism to avoid split brain scenario, say run your automation scripts from Azure or AWS hosted monitoring VM.