If I have a client with one Hyper-V and 2 VM's in it what should I need to have?
Yep, it’s possible to install VB&R server either on source Hyper-V host or on any VMs that reside on that host.
it enough with one veeam server on Hyper-V 2012 -hyper-v to backup and replicate VM's?
In order to replicate your VMs you’ll need to have an additional Hyper-V host, since only a host can be chosen as a target for replication jobs.
Can someone explatin what does Offhost backup proxy do?
The on-host proxy means that all of necessary VM processing operations will be performed directly on the source Hyper-V host. While off-host one allows you to take this workload away to a dedicated physical machine (“offhost proxy”).
When should I have one and is it needed?
Under certain circumstances, usage of onhost proxy may result in CPU/network overhead. So, if you see CPU or network being highly saturated, it’s a high time for you to think about offhost proxy utilization.
More detailed information can be found in the corresponding user guide (p. 26).
Hope this helps.