Hey there @jotemka! Welcome to the community! Let's see if I can't answer these for you...
a) i want to have a 2 columns in a container in different wide - but i want it overlapping like the screenshot i add. is there a possibility?
Using the columns stack in that fashion isn't a possibility on its own. You'd need a tool for creating the overlap. I do have something planned for overlapping elements though, but it just isn't available as of now.
b) i want on desktop in the nav-bar the rw-sitelogo (works) - on mobile no logo but the branding text?
That isn't a possibility with the Navigation Bar stack. Sorry.