The problem with the crossing of the solid yellow is that in many states, it's not specified. I'm in Ohio where it is, if safe to do so. A twisty road where you can't see far enough ahead wouldn't qualify. A cop may allow it if he sees it, but that's not the same as allowed by law.

As for large groups, I think it's also partially how large of a group. If for example there's a large turnout for a Ride of Silence, it would be prudent and reasonable for the ride to break up into groups of about 20 or fewer. But even that is a fairly large group.