You can only have one queue per interface and direction (one outbound queue and one inbound queue per interface). However, some queues allow you to have classes which can also have their own queue. Have a look at our QoS documentation, it is all explained there, and let us know if there is any doubt.
But it looks like you are trying to do shaping per client through [PPPoE Server](PPPoE Server — VyOS 1.4.x (sagitta) documentation. If that’s your case, check this.