if time is the fourth dimension it should be possible to move in several directions in time for a four dimensional being, time adds only two sides.
in my opinion multiple timelines and time are either the fourth dimension or not a dimension at all if we keep the dimensions spacial.
about the free will, we have some wiggle room and maybe by wiggling we are moving through the multiple timelines, it's just not that big of deal which timeline I'm on, the one that I posted this comment or the one I canceled are so similar in everything else I wouldn't notice I changed lanes.