A a table with benches.... when sitting on said benches...would you expect to be able to sit on either side exclusively without the other end coming up?

I'm gonna say yes!!!_

Yes.  But I know a couple that are so old they don’t function properly anymore and it’s almost a game - 4 people must all sit at once, and get up at once, or someone is going down.

Yes! But I've been on some really sketchy ones that will make you question the craftsmanship lol! 

If the base "legs" are properly placed, yes. If they are tucked in more than 8'ish inches, no.

Yes, absolutely. 

We have a bench on one side of our table. It's not attached to the table you can sit on the very ends of it & it doesn't ip up at all