If you know how the use the random dungeon tool, then you know that you can simply keep doing random dungeons over and over with the same group. AT THE MOMENT the tool is broken, so that if you do not have at least one random/new person in your group, if you get the same dungeon twice, it will already be cleared.

As for your other questions about how to do heroics with your team, there is a subforum for instance questions. I suggest a search of that forum. All heroics are doable, and become quite easy actually with experience.