How do you configure a 4-node AlwaysOn cluster to have two listeners?
is there a way to configure to have two listeners


Sort of, but it's unusual.  The more normal practice is to have a single AG Listener, with read-only routing configured.  That way everyone connects to the same hostname, but read-only workloads will disconnect and reconnect directly to an available readable replica. 


  would SQL on all four nodes need to run under the same service account?


It's recommended, but not required, to use a single Group Managed Service Account for all the nodes.  If the instances have different service accounts, Kerberos won't work when connecting to the AG Listener.