If your 5 VMs are directly connected to the internet, assigning them individual IPv6 addresses will work as per any standard guide without issue.
If you have an internal host only network (as I do), you need a firewall VM to handle the connections to your VMs on your internal network.
Following standard guides to get IPv6 up and running on a debian firewall should cover the basics. Use
https://code.google.com/p/npd6/ to force your firewall VM to answer to all IPv6 addresses in your /64 prefix. This is needed as OVH only route the prefix up to your box, without it your firewall will only respond to its assigned IPv6 address and you will not be able to use global IPv6 addresses within your internal VM network.
npd6 basically makes your firewall tell the OVH network that it is using every IPv6 address in your prefix, your firewall will then forward the traffic to the relevant VM on the internal network as per the normal IPv6 guides.