<human>: Give me the gist of the text in a nutshell

So my So and I had chosen our wedding date 21st Nov 2015. This will be our 4 year anniversary to the day. *insert happy dance*

We were speaking to my FMIL and found out that his 15 year old sister has national dance comps on that day. (HUGE deal to the sister and mum)

Now there is no budge room at all for her. She would have to miss the photographs and only be there *maybe* for the ceremony and reception. Now I had already asked his sister to be in the wedding around two months earlier but it seems like that doesn't matter to them. 

I'm SO SO upset that they are choosing dance over our wedding. I really don't want to go all bridezilla on their asses but I just couldn't fathom getting married without them next to me. 

I was talking to my FH about moving the date forward to March/April 2015 but he is against that idea due to "finances", now we have the money for the wedding now but it would chew up all of our savings and we really want to avoid that. 

His mother has already mentioned that they would help with the wedding, but have not said how much at all. I said to my FH that we should sit down with them and say that to make everyone happy we will move the date forward but we would need help financially. He was REALLY against that idea though. 

Please help!!!! I'm so upset and I just need some other opinions that are not so emotionally attached to the situation.
<bot>: Sister has dance commitments on our wedding day and would have to pull out of being bridesmaid. Should we move date earlier with financial issues or tell them they will have to choose.