They get around free will by, well, just straight up not violating it directly. Twinning the universes is a different sort of paradox (or did Odin say apocalypse 🤔 )
Take the events of DB. Harry was supposed to die in that Alley. He didn't specifically because of Kumori getting Marcones attention reviving the thug on Wacker St. Which I know, should be paradoxical in itself. But why wasn't it? Because the thug was never supposed to die. We've already seen another prime example of someone messing with perceptions to get two groups to shoot each other, when the Rag Lady was operating. So, she does something to cause a shoot out(which works really good as a future Alt version of Molly btw) and then something spectacular to draw attention to it's oddity. This cascade's into Marcone making the choice to go meet Dresden and save him in the Alley. The rules have already been laid out, you just have to look for things that fit.
The funny thing to me, is Kumori does that minutes before they show up together at Bocks. I think if Harry had died in the alley, there wouldn't be a body left to revive. So cowl didn't exist when fate was on that path, only Kumori. Timeline flux with each intervention changing who went back from where and what they changed,