Ok, I genuinely want some opinions and and to see if anyone else has been in this situation.
I have a 4 month old baby and my BIL is getting married in December, my DP is best man.
The wedding is to be a huge Irish shindig, you know the score, 300 guests, mahoosive posh hotel etc etc.
I was initially so excited, but am now dreading it.
It is a 2 hour catholic service - and I am expected to stay there for the duration - I politely asked "DS is unlikely to stay still and quiet for the service, is it more important for me to be there at the beginning or end?" told, be there for the whole thing as you can stand in the side or go outside if he gets restless. 
Main issue however, is the six course dinner. I am not allowed at the top table, and I do not know anyone else to sit with. When DP asked his brother if he could sit with me and DS, he was told "no. absolutely not. I need you next to me, and if you cant do that, then i will ask someone else to be my best man" DP was really upset by this reaction, explained that he wanted to help me with our son, crawl control, feeding etc. BIL replied "she looks after him on her own everyday, whats the big deal?".
So I will be eating on my own, trying to control DS, then going to bed with DS at 7. Great.
I have to take him to Ireland as its the inlaws chance to see their grandchild at Christmas, and I cant leave him with anyone there as i dont know anybody, and he is EBF.
Aaargh! Really dont want to be the awkward one, I am fine with the 4 day stag, but what can I do???