You are in the trenches here...see it? I pray for the best results for God here and that peace overtakes you in what you end up doing. This guy is going thru his own moment of crisis God has allowed. And although it seems like something God need not worry about, that is Satan's lie. God is about the business of all the in-between moments of life. So I see a great opportunity to witness, simply in how you handle it. In the right and wrong department, yes he has overlooked you, and other people in the group, but instead of correcting his right and wrong in it, minister to him the love of God. Satan wants you to see the 12 year old here. God wants you to see a place where grace can move a 34 year old man{name here} in crisis toward Him.Authoritative Wisdom quietly left behind is affective whereas loud correction of rightness, or a cleverly soft sarcastic correction usually simply creates separation, and hardening of heart.
Satan says, "This man is wrong even by Gods standards, You have a right here!" God is saying, "Look a place we can have an impact, if you let Me I can serve this man who is acting like a child, it may cost you your right to be right, but I would show my supernatural unconditional love if you make way for it." Your choice! There is no condemnation in Christ, yet, there is a way that is better than other ways in serving Gods glory, over our own truly given rights.
Your future meeting has a choice, humans will never think you wrong to take what is rightfully yours, you have indeed made correct choices in the plans you have made. But I would pray, "Lord, how can you be glorified in this, help me know how I can serve both you God and this man in crisis, and show me, and everyone the lengths you love people in the small things of life, in this moment in time with this over-aged man.." I threw a bone for your rights in the prayer did you get that?!! Smile.
You sister need not be about this emotionally. You are not in error., either way .You can be at peace, the only thing you need to act upon is Gods lead. Slow down a touch and clean-slate the mind and get back into that peaceful mind-set knowing there are no wrongs placed on you... and I know God will have you deliver a response in real time, then, that will be His chance to work from there, at that moment simply say yes to God, and you remain in peace the whole way threw this snitbit of time, yet God will be left behind in a great way. Just saying....
I have all sorts of suggestive options personally to the specifics of what to do...reasons why you should not change the time, reasons why God could have you do that in a certain way, etc etc...but it isn't about our right answer is the point. It's about His, That has a fluidity about it depending, now, on your discernment in Christ. people can help you direct His will but God is the engine of all your decisions. Trust yourself in that place. God does, I do, we all do. For you are indeed a Christian.