I hope you will forgive me for jumping in, here, but I wish to suggest that it would be useful for your discussion, to agree upon a definition for your terms. "Free will" is a term that, in my experience, is not clearly defined.
A well-known philosophical riddle is: "if a tree falls in the forest, and no one is there to hear it, does it make a sound?" It seems to me that the answer to this question depends upon what is meant by "make a sound." If one means, "produce sound waves in the surrounding air" then we can expect that the answer is yes, assuming constant natural laws; if one means, "produce a hearing sensation," then the answer is no, since it has been stated, as part of the question, that no one hears the tree fall.
"Will" may perhaps be regarded as synonymous with "intent," and I suppose that it is likely that there can be agreement with the proposition that human beings can have intent, and act according to it. "Free" means "without constraint" and it may be presumed that "constraint" would include "necessity to act as an effect, resulting from a cause," so that "free" would mean "having no cause" or "undetermined." Alternatively, this may not be what is commonly understood as the meaning of the word "free" in the context of "free will;" it may instead be that "free" means "not having been caused by a thing or event that has been specified."
"Reason" assumes determination by logical implication (logic is a methodology designed for achieving accurate inference), and "science" tends to assume predictability (including, by comparitive probability), since its basic intent seems to be to understand phenomena and to be able to explain and predict their behavior. This makes the whole issue of "free will" perhaps insoluble by reason or science.
Anyway, I suggest that your debate is likely to be successful in reaching some reasonable, agreed-upon conclusion, only if you start with agreed-upon premises/definitions of terms.
As an aside, I will also suggest that one should be careful about using the words "science" or "scientific." Science is not characterized simply by the use of reasoning; it is defined by the Scientific Method, which necessarily includes the experimental confirmation of any hypothesis - reasonable, or not.