You can use the ‘move’ function in Hyper-V to perform a live migration which incurs no downtime. Select the VM, click Move, select ‘Move the virtual machine’ (not ‘Move the virtual machine’s storage’, that only moves the storage, not the whole VM), and then finish out the wizard. IIRC that is sensitive to host architecture being sufficiently similar (changing processor generations can make it sufficiently different), so it may not work for you.
If you can’t do that and since it is a single-digit number of VMs, you could turn them off, copy the .vhd files to the new location, set the VMs up on the new server, and turn them on. That is, of course, going to incur some downtime, so it isn’t optimal.