Then might I suggest that the best thing we can do with him is not have chatty conversation about this and that. The only thing we should do is present a united Christian front with him: "Repent and Believe!"
I know you have discussed with him before; he doesn't need to discuss Arminianism vs Calvinism, he needs Lost vs Saved.
I am Saved, that makes you ... what?
It is time, at the end of the thread, after all these denials, to restate the things that are true no matter how many times you all deny them, and even if I am the only one to uphold them:
I have accepted Jesus Christ as my Lord and Savior. I have taken His name upon me. I am born again. I am regenerate. I am a Christian. I have been ordained to preach the Gospel and administer the ordinances thereof. I solemnly testify that Jesus Christ is our Lord and God, our Redeemer, our King, who atoned for our sins, broke the bands of death, and made eternal life possible for us. He will come again, as the ancient apostles saw him go into heaven. He has sent apostles and prophets and additional Scripture to the earth in our day, as it is His prerogative to do.
Don't be excessively distracted trying to understand things before the foundation of the world, once you know who you are, a child of God, and that you are accountable before Him for your earthly stewardship.
Focus on the things you are to learn and do here, in particular mastering the Christlike attributes of character, the things you were taught from kindergarten age and before:
Faith, hope, love unfeigned, virtue, humility, meekness, courage, the Golden Rule, patience, godliness, temperance, diligence, brotherly kindness, faithfulness, trustworthiness, and so forth.
May the Lord's rich blessings be with you all!
Numbers 6:24-26
24 The LORD bless thee, and keep thee:
25 The LORD make his face shine upon thee, and be gracious unto thee:
26 The LORD lift up his countenance upon thee, and give thee peace.