Most of that is Waid's fault. He made an evil twin for Barry. He made Impulse. He made Impulse's evil not-really-anything-like-him clone Inertia. He didn't make the Tornado Twins I don't think, but he certainly took advantage of the idea.
Being related to Barry means having a thousand relatives, most of whom will time travel to make it with the few people they're not related to.
All we need is a Flash to vibrate over to Marvel and sex up a Summers and the Big Two will implode.