Permissioned nodes indicate which nodes are whitelisted for connection.
There is no validation of the list of permissioned nodes at the network level, each node operator sets their own permissioned nodes list.
Since it's a peer-to-peer network, if your node can connect to any node on the network, your node can receive all the blocks.
Yes it is possible. That said, Quorum permissioned model enforces authentication by validating immediate caller (whoever is at the end of the TCP connection), if two nodes have each other in the permissioned file, discovery is enabled or they are in the static file as well, and they have a communication channel (E.g No firewall blocking), then they will be ...