Tvheadend

Hello Guys!

I'm trying to understand how 2 or more tuners are handling only 1 subscription... Can this be handled?
Is this a thing I've to set up within oscam, cccam or tvheadend itself? Any hints where (or in which config) I have to search for this?
I'd like to understand how this stuff works, but this doesn't seem so easy...

Because it's possible, to use 2 channels at the same time with only 1 tuner (as long as they are on the same transponder)... now the thing is, how is this handled with only 1 subscription?
Uses tvhe always automatically the first available subscription for a selected channel? Could it be, that 2 tuners trying to use 1 subscription at the same time, altough there are 2 subsriptions?
What happens, if I've 2 tuners with 2 subscriptions?

Oh my god...

Thanks a lot!