Sorry for my ignorance regarding that denomination, I belong to PCA and am a fairly new member. I don't know that particular splinter, but it doesn't mean I or all Presbyterians believe in the kind of heresy you described.
For the record I am defined by my personal relationship with my savior, not my relationship with religion. My assumption is the same for you, and in that regard we are much closer as His children, than any false separation created by a particular religiosity or doctrine. Beyond that, I believe wholeheartedly in the Apostle's Creed -- and in Romans 8:26-30. I know you do too.
In advance I apologize for not answering every point, but RL beckons and this post is too long as it is.
I'll address your final point, then try to wade through the rest. When we get into an area of the Lord's "willing"ness we should proceed with caution, lest we blaspheme. The Holocaust was not within God's will, was it? Yet it happened; as believers we realize His omniscience would not allow for His ignorance of a future event, and His love and holiness would not allow Him to PERPETRATE a Holocaust. Even so on an individual level, it is not His will that any should perish. Yet He allows it to be so, and with foreknowledge.
One could argue that if it is not His will that any should perish, then those whom He knows in advance will deny Him should never be born in the first place. We both know we have no rights within that argument - God would answer as He answered Job.
What then of free will? Either He created us with free will, and allows us to exercise our free will, and suffer the consequences, or He doesn't. But how imperfect is our true understanding of free will within this context: either God is Sovereign, or He isn't.
Indeed: 28 And we know that God causes all things to work together for good TO THOSE WHO LOVE GOD (not, "to everyone"), to those who are CALLED according to His purpose (not, "all of humanity"). 29 For whom He FOREKNEW, He also predestined to become conformed to the image of His Son, that He might be the first-born among many brethren; 30 and whom He PREDESTINED, these He also called; and whom He called, these He also justified; and whom He justified, these He also glorified. NAS
Would he CALL, conform to the image of His Son, justify, and glorify the body of Christ (the invisible church), and the individual believer, if something as frail as a human being's free will could interfere with His ultimate plan for that individual or the body of the Church?
"My sheep hear my voice, and I know them, and (they follow me And I give unto them eternal life; and they shall never perish, neither shall ANY MAN pluck them out of my hand." John 10:27,28
Peace.