Notify owner of post and other commenters
First of all I would add a method to Post:

# app/models/post.rb
def notify_others_about_new_comment(comment)
  recipients = [user]               # the author of the original post
  recipients &lt;&lt; users               # people that wrote a comment
  recipients.delete(comment.user)   # writer of the new comment

  recipients.uniq.each do |recipient|
    Notification.create(
      recipient_id: recipient.id, 
      sender_id: comment.user.id, 
      notifiable: self, 
      action: 'commented'
    )
  end
end


And just call that method in your controller:

if @post_comment.save
  @post.notify_others_about_new_comment(@post_comment)
  #...
end