The fifth commandment says, “Honor your father and your mother, that your days may be long in the land that the Lord your God is giving you” (Exodus 20:12).
Nowhere in the Bible does it differentiate if one's father is "in The Troof" or not so. Your brother cannot even apply any defense of "apostasy" or "inactivity" as if your father was a "weak" or former JW. Also, consider Paul's view of those who have no affection for their parents:
2 Timothy 3: 1 But know this, that in the last daysa critical times hard to deal with will be here. 2 For men will be lovers of themselves, lovers of money, boastful, haughty, blasphemers, disobedient to parents, unthankful, disloyal, 3 having no natural affection, not open to any agreement, slanderers, without self-control, fierce, without love of goodness, 4 betrayers, headstrong, puffed up with pride, lovers of pleasures rather than lovers of God, 5 having an appearance of godliness but proving false to its power;b and from these turn away.
BEAT HIM WITH HIS BIBLE