How to make more than 1 nodes of mine connect each other? Lets say i have 5 nodes running.

each node is on its dedicated server and is upto date. and its connected to available peers on the network.

How can i make them to connect each other and not to BAN them, and connect them again in case of bitcoind restarts ?

so in case i plan to make star topology of nodes and use central node for RPC connections.
You can add them to each other nodes bitcoin config file. If you want to connect to a specific node among others, use addnode=IP:PORT in your config. If you'd like to only connect to your own nodes and not other nodes on the network, you can use connect instead of addnode, but of course you should have at least one outgoing connection to get blocks, etc :)