Format nested JSON object from Postgres query

I want to get a JSON object formatted similar to this:

{
  "username": "USERNAME",
  "teamname": "TEAMNAME",
  "logs": [
    {
      "log": {
        "log_id": 29,
        "person_id": 3,
        "activity_id": 3,
        "shoe_id": null,
        "logdate": "2016-11-29",
        "distance": null,
        "activitytime": null,
        "sleep": null,
        "heartrate": null,
        "logtitle": null,
        "description": null
      },
      "activity": "Swim", 
      "comments": {
        "comment_id": 1, 
        "description": "This is a comment", 
        "person_id": 1,
        "log_id": 29
       }
   }]
}

Currently I have everything formatted correctly except the comments. Here is the SQL query I am using:

SELECT p.username, t.teamname, json_agg(json_build_object('log', l.*, 'comments', c.*, 'activity', a.activity)) as logs
        FROM person_tbl p 
        INNER JOIN log_tbl l ON p.person_id = l.person_id 
        INNER JOIN activity_tbl a ON l.activity_id = a.activity_id 
        INNER JOIN comment_tbl c ON c.log_id = l.log_id
        INNER JOIN person_team_tbl pt ON p.person_id = pt.person_id 
        INNER JOIN team_tbl t on t.team_id = pt.team_id 
        WHERE t.team_id = 5
        AND l.logdate > NOW()::date - 7 
        GROUP BY p.username, t.teamname 
        ORDER BY p.username

I'm having trouble getting the comments of each log. Right now, it is returning every comment and repeating the logs (they are not associated).

Also, how could I get this query to return the username and teamname when everything else is null (like when there are no logs in the past week)?