You only need the RoC key linked to Battlenet. It alone will unlock all of the Classic mode of Reforged, RoC and TFT. Note: The TFT key alone will do nothing when linked to a Battlenet account. It has to be the RoC key.
In Reforged, the two campaigns have been merged into a single, long campaign. So, to get to TFT, you need to use a cheat code to jump to the start of TFT.