there are creatures with free will
Probably not. What we have is the illusion of free will - the experience that we have an urge or desire that we can and do indulge.
But that is not free will. That is merely serving as the conscious overseer of a process that he did not initiate. Neural circuits measure the osmolality according to the degree of concentration or dilution of the blood (variation from normal), decide that it is too high, that the body needs water, and sends a signal to the consciousness to seek a drink. Assuming that there are no barriers to drinking, one gets a drink.
As far as we know, there is no free will there - just the illusion of same. You didn't choose to be thirsty. The conscious self is not the source of the will, merely a recipient of its instructions.
You might say, "Ah, but yes, I can choose not to drink." Not without a second, more powerful and conflicting message delivered to the conscious self that one wants to refrain from drinking for whatever reason - perhaps to "prove" to himself that he has free will.
What most people mean by free will is that the conscious self is the author of its desires and choices rather than being a passive recipient of and conduit for unseen neural circuits connecting desire to action, that is, that these desires and choices are uncaused by material neurological mechanisms and have no prior cause originating outside of consciousness.
That's impossible. No conscious experience is uncaused, and the source of any sensation, thought, feeling, or urge is always outside of consciousness, precedes consciousness, and informs consciousness.
if God doesn't exist there wouldn't be creatures with free will
You haven't defined what you mean by free will, which is likely what I have called the illusion of free will, where one doesn't realize that the self, by which I mean the observer in the theater of consciousness distinct from brain functions informing that self through conscious phenomena, are not the source of one's will or decisions.