Hello,
WC3 Standard Edition includes two CD-Key “Roc & TFT”?
no, the frozen throne`s cd-keys is no more. now there is only reign of chaos cd-keys. the versions of the game was merged into one and you can switch between them from the menu.
So, I can play TFT Battle net with ROC CD-Key?
yes. you are able to do that.
I dont know, I think if you are using an original RoC CD-Key then you would probably still need the TFT cd key to play online, but Im not sure. I know RoC no longer works online tho 
if you buy Reforged you get access to classic TFT for free, but I dont think classic RoC owners get TFT free
There is no facility to enter TFT CD Keys anymore, hence they clearly are not required for online anymore.
I think they do. If this is legal or not I cannot tell, however nothing mechanically is stopping someone with RoC only from playing TFT as the Warcraft III installer installs both and only asks for the RoC key.
It also is no longer possible to buy fresh copies of RoC or TFT by themselves, since only Reforged licences are being produced and that automatically includes both on top of Reforged itself. I would not be surprised if any RoC and TFT CD copies left unsold in shops end up in bargain bins for 1$ or so.
This points towards a future model similar to StarCraft Remastered where by the base game will be made free to play while only the HD graphic pack (and remastered campaign and features) will cost money. Very annoying for loyal fans who have treasured their RoC and TFT CD Keys for ~15 years. Fantastic for new people to get into Warcraft III, especially at the current price.
Bliz broke RoC and gave everyone with RoC TFT for free. Yes, RoC is all you need. Did you forget?
No one cares about RoC lol
i have tested the old keys myself and online works with only the reign of chaos cd-key.