Are torchlight 2 and 3 work together?
Solution 1:
No. You can't play together as the two iterations of the game are incompatible with each other as they are completely separate games. If you all want to play together, you must all be playing Torchlight 2 or Torchlight 3. Not both or a mix; it's one or the other.
It's like trying to play Halo 1 multiplayer with Halo 4 (Master Chief Collection does not count).