I sympathize with your Mum but am on your side . The venue and date is booked so stick to your guns. Your brother seems ok about it so in my view there is no problem. I fully understand why your Mum wants her son to be there , but he has changed his job and that is the reason he can't make it - not his fault but it is what it is. Planning a wedding is a stressful occupation and you can do without this !! and who knows , June is some way off and your brother may be able to sort it out. If not then so be it. Your dear friend is MOH and that should not be compromised. I am sure your brother would not expect you to change your plans just because he can't be there - with respect to your Mum neither should she! Please don't try and defend your position you should not have to do that. Have a wonderful June wedding, we married in June - 50 years this time !! I wish you every happiness. Go ahead with your plans, your Mum will come to terms with it . Good luck.