Each Dgraph instance needs a configuration in accordance with parameters like -o flag. As you add -0 2 you need to put all ports +2 offset. eg:
dgraph zero -o 2 --my=this-vm-ip:5082 --peer zero-leader-ip:508? --idx 3
dgraph alpha --my=this-vm-ip:7082 --lru_mb=2048 --zero=zero-leader-ip:508? -o 2
https://docs.dgraph.io/deploy/#cluster-checklist
BTW, you can’t choose who the leader is. This is decided via algorithm.