Expanding AlwaysOn Availability Groups with Replication Subscribers
Can I add multiple publishers to a subscriber(which is part of
  availability group as a primary server)?


Yes, this is the multiple publishers model and is supported.


  In which node can I configure distributer?


The distribution database is currently not supported for use in AlwaysOn Availability Groups. The only supported method for transparent distributor failover is AlwaysOn Failover Cluster Instances.


  How do I configure the distributer?


You can configure it through SSMS or T-SQL.