Notification of new comments for author and comment writers
Have a look at this rule (in Rules export format), which does what you're asking for:

{ "rules_notify_users_about_new_comment" : {
    "LABEL" : "Notify users about new comment",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "rules", "rules_conditional", "comment" ],
    "ON" : { "comment_insert" : [] },
    "DO" : [
      { "variable_add" : {
          "USING" : { "type" : "list\u003Cuser\u003E" },
          "PROVIDE" : { "variable_added" : { "users_to_notify" : "Users to notify" } }
        }
      },
      { "LOOP" : {
          "USING" : { "list" : [ "comment:node:comments" ] },
          "ITEM" : { "current_comment_item" : "Current comment item" },
          "DO" : [
            { "CONDITIONAL" : [
                {
                  "IF" : { "NOT data_is" : {
                      "data" : [ "current-comment-item:author" ],
                      "value" : [ "comment:author" ]
                    }
                  },
                  "DO" : [
                    { "list_add" : {
                        "list" : [ "users-to-notify" ],
                        "item" : [ "current-comment-item:author" ],
                        "unique" : "1"
                      }
                    }
                  ]
                }
              ]
            }
          ]
        }
      },
      { "CONDITIONAL" : [
          {
            "IF" : { "NOT data_is" : { "data" : [ "comment:author" ], "value" : [ "comment:node:author" ] } },
            "DO" : [
              { "list_add" : {
                  "list" : [ "users-to-notify" ],
                  "item" : [ "comment:node:author" ],
                  "unique" : "1"
                }
              }
            ]
          }
        ]
      },
      { "LOOP" : {
          "USING" : { "list" : [ "users-to-notify" ] },
          "ITEM" : { "current_user_to_notify" : "Current user to notify" },
          "DO" : [
            { "mail" : {
                "to" : [ "current-user-to-notify:mail" ],
                "subject" : "New comment to node with id [comment:node:nid]",
                "message" : "There is a new comment added to the node with id [comment:node:nid]",
                "language" : [ "" ]
              }
            }
          ]
        }
      }
    ]
  }
}


I translate the "... in the same rules ..."-part of your question like "I want it to be a single (monolitic) rule". For that you'll need an additional module, i.e. the Conditional Rules module, while the above rule does use a few of the more advanced techniques available in the Rules module.

If you're familiar with reading/digesting Rules in Rules export format, I'd hope the rule is self explaining. If not here is a summary of the above rule:


Rules Event: obvious ... After saving a new comment.
Rules Conditions: feel free to add whatever fits (eg limit to selected content types only).
Rules Actions:


Add a variable "users_to_notify" (= a list of users).
Loop over all existing comments, and for each comment author, check that it is not the user who just created the comment (which you can check if you have the Conditional Rules module enabled). If that's the case, then add that user to the list of users (= users_to_notify).
If the comment author differs from the node author (which you can check if you have the Conditional Rules module enabled), then also add the node author to the list of users (= users_to_notify).
Loop over the list of users (= users_to_notify) ... again, which we just created and populated). And for each user in that list, do your thing, in this case "send an eMail". The "To" value is crucial here, the body, the from, the title, etc is up to your own imagination.



If you don't want to use the Conditional Rules module, you could also rework the Rules Actions that require this module to performing Rules Components (in which you add the appropriate Rules Conditions), so that you don't need this extra module (for more details on that, refer to the answer to "What&#39;s the alternative to using the Conditional Rules module?").

If you want, just import the above rule in your own site (using the Rules UI, which should be enabled to do so), but only after you enabled the Conditional Rules module.

That's really all it takes ... a Rules variable, Rules lists and loops, and Conditional Rules.

Note that the above rule does actually more as compared to what is asked here:


As per the "unique" in Rules Action nr 2, it will not create duplicates in that list of users, to avoid the same user would receive duplicate eMails (i.e. if a user commented multiple times).
As per the "unique" in Rules Action nr 3, it will not create duplicates in that list of users, to avoid the node author would get duplicate eMails (i.e. if the node author also commented already).
This rule will NOT send an eMail if the comment was posted by ... the node author (which seems to me like a contradiction in item 1. and 3. of the question ...). If you disagree on that (i.e. that it should send an eMail anyway: just delete Rules Action nr 3.


Unit testing the rule

If you want to (unit) test the above rule, you may want to add another Rules Action within Rules Action nr 4. I.e. add some sort of "Show a message on the site" (located within Rules group "System"), to produce a message for each user included the list of users (= users_to_notify).

That way, if for some reason your site has not been correctly configured yet to send eMails, those messages will help you confirm that the rule itself is not the cause of that.

Video tutorials

For anybody not familiar (enough/yet) with Rules, checkout the 32 (!!!) great, and free, video tutorials Learn the Rules framework, organized in 7 chapters. Especially these tutorials, which are related to subject of this question:


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