Las Virgenes Rd - Malibu Canyon Road in LA County

Unless you are super comfortable on winding mountain roads I would definitely avoid both those routes. Malibu tunnel would be a tight drive. Both roads have shear drops and both are heavily traveled by car commuter traffic. Going a bit wide on a turn and crossing the yellow could find you with a sports car (Ferrari) or motorcycle in your lap. Given your size go the long way...take the 405 and exit Sunset, turn right and it is a straight shot to the 101, from there it is not far to Malibu. Even in a car it is our preferred route to the beach.
Happy Trails.