@Visionary If the game supports local multiplayer then you should be able to have multiple controllers connected to the same game session (so I think the Samurai Shodown scenario should work - though I'm not 100% sure if that's been implemented yet). But you can only have one active session per account which would rule out the Destiny 2 scenario.
There is some information in the FAQ:
How many controllers can I use at the same time?
Your Stadia account will support up to four Stadia controllers during local multiplayer game play.
I am a Founder and have redeemed my code to access and create an account on Stadia. Is there a limit on how many compatible devices I can use?
You can play on any compatible device, but you can only have one session active at a time across all your devices.
@Visionary If the game supports local multiplayer then you should be able to have multiple controllers connected to the same game session (so I think the Samurai Shodown scenario should work - though I'm not 100% sure if that's been implemented yet). But you can only have one active session per account which would rule out the Destiny 2 scenario.
There is some information in the FAQ:
How many controllers can I use at the same time?
Your Stadia account will support up to four Stadia controllers during local multiplayer game play.
I am a Founder and have redeemed my code to access and create an account on Stadia. Is there a limit on how many compatible devices I can use?
You can play on any compatible device, but you can only have one session active at a time across all your devices.