Diablo 1 HD Hellfire Mod | Awake

I've read something about being in a party in a torment game in order to gain access to the 5 new recipes in Tchernobog in discord.
Now do the recipes drop in a multiplayer game while NOT playing with someone?
Or does it mean that you must at least team up with someone else to make it even possible to drop?

The latter. Additional players in the game increase monsters' level, thus making them possible to drop better loot. Though there is a very slight chance of finding those new recipes in solo play by killing rare monsters with extra level mod. But this is much less likely than killing torment diablo in party.