Trinitarian Christology and the true humanity of Jesus vs. Calvinism

I came across this insightful comment from a Catholic apologist offering his review of a debate on predestination/freewill (available here). I think the questions he poses to Calvinists, who hold to the hypostatic union, shows the impossibility of their theology (square bracket added for clarification):

Adam [prior to the fall] was not subject to sin, yet chose to disobey God. At this point, it's proven that free will and predestination can co-exist. White recognize this 'problem', and had to be as vague about Adam's will as possible. If White would have denied Adam's free will, then he would be saying "sin" and the fall have nothing really to do with this subject. 

From there, Sungenis *SHOULD HAVE* gone Christological on White, and asked if Jesus had free will. White couldn't say no to that, and thus the door would be slammed shut, since Jesus is the synthesis of freewill and predestination. Sungenis and White didn't seem to be aware of how to go about discussing this issue, especially the notion of "human nature" since "human nature" must be what Jesus took on and which Adam and we all possess as well. And since the heresy that Jesus only had one will was condemned by an Ecumenical Council (since will is a function of *nature*, and Jesus had two natures), Sungenis should have emphasized this as well.