everybody talks about Will flipping his lid over the death sibs or Jason not being vaccinated or similar, but I think the true thing that would make Will nearly pass away on the spot is finding out that Hazel has a completely unaddressed fainting condition that may or may not be seizures that she has absolutely never gotten checked out in any capacity and just kind of shrugged off when they "stopped."
look me in the eyes and tell me Will wouldn't absolutely lose his shit that Hazel has NEVER gotten it checked out or even went to anybody after collapsing in case she hurt herself while falling. He'd be getting her a medical bracelet asap.