Just in the last year, we are now seeing flashing yellow left turn arrows. It certainly has confused people. Basically, the solid green arrow still means "you're the only one who can go now". But when the cars coming from the opposite direction get a green light for all lanes, that left turn arrow changes to flashing yellow. It's supposed to mean "you can go, but yield to oncoming cars". Many people hesitate to go at all.Did they have a turn arrow by chance? I know we have a big problem here with people understanding when to yield in those situations.
As for two cars turning, yes, the left turners are supposed to yield. In a two lane situation, most of the time people will take turns, because they don't trust the other driver to turn into the nearest lane. I force them to do that, or to hit me. So far, I haven't been hit.
Also love how people merging onto the freeway think that they can drive whatever speed they want, then the cars in the right lane should adjust their speed or move over so they can get in at the end of the merge lane. Way back in the last century, I was taught in Driver's Ed to maintain my speed on the freeway, and the merging driver should adjust his/her speed to match the flow of traffic. Good luck with that one! Sometimes you can't move over because of traffic. You're not required to do that either.