IMHO, I think it's possible for Jesus' two Wills to be in opposition. I believe Christians have some small measure of the Divine Will through the indwelling of the Holy Spirit. It's not a full measure, so we don't know the exactly what the Divine Will wants and we can't actualize the Divine Will to perform miracles, but it's there a little bit. Even so, our human wills constantly war with whatever measure of the Divine Will we can access. Paul was more immersed in the Divine Will than us as evidenced by his prophecy, miracles, and penning of Scripture, but he still notes conflict between this and his human frailty. You can look at the very name Israel the same way. It means to "struggle with God" and pretty accurately describes the conflict between God's Will and human wills in both the Old and New Covenant. So the idea of a possible conflict in Jesus' Wills fits right in that pattern.
Or to look at it another way, the Divine Will is ultimately free. It can do anything without limit. The human Will is limited in some ways by the Divine Will, but humans still have some limited free will that can oppose the Divine Will. If that weren't true, then there would be no human will. There would only be limited iterations of the Divine Will. If Jesus' human will could never contradict or conflict his Divine Will, then it wouldn't make any sense to say he has two Wills. The human will wouldn't matter at all.
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