Most roundabouts that I encounter are one lane, not two. However, in this case the rules would be the same as any two lane (same direction) road in that the yellow car is allowed to turn off only if the adjacent lane is clear. If not, simply go around again.
We have a two-lane roundabout not far from where I live. When I was an apprentice, that same roundabout was a three-lane job......lots of fun.
Basically you start moving towards your outer lane after you cleared the ones that peel off before your exit. It is easy once you get the hang of it.
In the wet that roundabout used to be lots of fun....I did at least 2 180's on it way back when. The traffic usually stops well short.
That same roundabout has now been turned into some weird sort of concoction of a Y-junction intersection to accommodate a new Bus Lane route. It has completely taken away the plot of grass where we had a magnificent tree with Christmas lights each year. Our company had the contract to hang the lights, and remove them every year. I did that at least twice in my lifetime. It was the only time we could legitimately drive on the grass.
Here is what it looks like just recently - stole the picture from the innerweb....
Here's an old shot after the tree was removed.....
Thís was taken just before reconstruction around 2 years ago...
The brown building on the right was a FORD Dealership called Panmure Motors. One day, Shaky Dave and I were given a job to repair all the fluorescent lights behind the huge letters making up the sign "PANMURE MOTORS". We removed all the letters and laid them down flat on the mezzanine roof extension to go off for morning smoko (break time), but just before we left, I rearranged a couple of letters and stood them up to read "MANURE MOTORS"
Shaky Dave didn 't know what I had done, until we were across the intersection stnding outside the Bakery shop that was our local haunt. I told him turn around and look. He just about shat bricks.....went apeshit at me....it was funny as hell.
My only regret is that I didn't have a camera on me....it was 1984.