Native speaker. Yes that would also be correct. But both sentences would be used in different situations though.
Where are you? Wer'e here, we zitten op de bank, we're on the sofa.
What are you doing? Not much we zitten op de bank. We're sitting on the sofa. Or in cases the sitting and or sofa is important we zitten/are sitting on the sofa not on the floor.
So in English you need to check the context. In dutch it works in both cases. (My examples might have scked but I'm sure you get what I mean. Especially if english is your native tongue you will know the differences yourself )
Not really sure what you mean with the English sentence. Sitting inside the bank (building).?
Both ik zit bij de bank as ik zit in de bank could work. Depending on exactly what you mean. (Definitely not aan) but I think it would be bij for what you mean.
You are at a place=bij inside it= in.
It could be, though there is a difference with the English kind of bank in that case.
In English a bank is typically the piece of land next to the river/lake that slopes into it. In Dutch however it would be a piece of land in the water that typically only would be visible with low tide (http://nl.wikipedia.org/wiki/Zandbank).
No it couldn't, you would say zandbank in dutch.
Only when you are a sailor/fisherman and you use the word several times a day I can imagine you would say bank. But I'm not sure they eve do that moreover if it would be officially acceptable. (We hebben veel banken moeten ontwijken.. It doesn't sound correct, even if I imagine having been on a ship my entire life)
Yes but more than 95% of the time bankje is used for bench. That is what people would say when you point and ask what it is.
Een "bank" might slip out on rare occasions and would still be correct, just not standard.
I can imagine when 2 people are allready sitting on a bench and the 3rd person (sibling/friend) would want to join you could get.
Scoot over I want to sit on the bench too.
Schuif eens op, ik wil ook op de bank zitten.
But like is said normally we say bankje