If you are only looking for a sketch of how you might travel in time without determinism, and you equate free will with determinism, then one can easily sketch a world which admits both free-will and time travel, and in which physical systems and events have apparent causes.
Allow me to sketch a bifurcating time-line admitting time travel. If we suppose that by and large matter/energy is conserved in the usual way, except when engaging in the mechanisms of time travel, then just because you have travelled back in time to kill your grandparent does not mean that you will stop existing. If you absolutely require chains of causality to be traceable over long stretches of time and beyond the process of time-travel itself, then it simply suffices for there to be one continuity (a) in which you are born, and another continuity (b) in which you arrive from the future:
Time t=-51.
Your grandparent meets their future spouse for the first time.
Time t=-50(a).
Your grandparents start a serious relationship.
Nobody particularly interesting appears from the past.
Time t=-49(a).
Your grandparents get married.
Time t=-25(a).
Your mother is born to your grandparents.
Time t=0(a)
You are born to your mother.
Time t=30(a)
You have invented a time machine, and travel back to time t=-50.
Time t=31(a)
Your disappearance remains an unsolved case by the police, and you are presumed dead.
Time t=-50(b)
Your grandparents start a serious relationship.
You appear from the past.
Time t=-49(b)
You kill one of your grandparents, preventing your mother from being born. Being a physical system which has a past which can be traced back some amount of time, and whose appearance in the past can in any case be explained by the mechanism of time-travel to a continuity in time in which this assassination did not occur, you continue to exist, because physics is not in the habit of simply allowing macroscopic physical systems to vanish.
Time t=-25(b)
You are freed from prison for your crime of murder, on parole, due to good behaviour.
Time t=0(b) You privately and wryly commemorate your own zeroeth birthday.
Time t=25(b) You celebrate your 75th in-continuity birthday.
Time t=30(b) You die in a car accident.
To an observer experiencing the world without a time-machine, they would with some probability observe time-line (a), and with some probability observe time-line (b). There would be a copy of that observer for each time-line, observing each; this does not require duplication of matter (or entire universes) in principle, and can be achieved in configuration space by a similar mechanism as the so-called parallel worlds of the Many Worlds Hypothesis of quantum mechanics.
You might complain that I don't give you any way to determine the probability with which a subjective observer would see you appear from the past, or that merely with some probability appearing in the past isn't good enough. I actually suppose that your time-travel mechanism is 100% successful, conditioned on you engaging it; but this doesn't mean that a past observer actually sees you emerge with probability 100%. You could more fairly complain that it's not clear how to interpret probability without ensembles or repeated trials, which would be a very good criticism in fact; but we don't have to suppose that there's any actual numerical probability attached. There is just a nondeterministic event in which a past observer either sees you emerge from the future or doesn't, and potentially either lives to see you born, or to see you kill your grandparent; and as a subjective participant you are assured of finding yourself emerging in the past.
Does this represent the freedom of event-space required for what you want to call "free will"? So long as you are identifying F ≡ ¬D, it doesn't matter — in this hypothetical physical ontology, nature is not deterministic, which (by your assumption) means that "free will" is true by definition.
Of course, this answer is entirely speculative; you have not actually learned anything about time-travel from this, except that it is possible to imagine a way that it is compatible with a non-deterministic universe.