We are getting married and FIL is terminally ill. We very much want him to attend so are looking at saturdays across a TWO month period this year
Everyone has been asked to tell us dates they cant do.
MIL has been stressing out/upsetting my fiance in verious ways recently (eg shouting/telling off poorly fil) but the latest is by asking us to move our wedding dates to suit BIL...?!
It alllll blew up tonight and i am so upset i cant sleep.
She wants us to push it out to next year (Fil is V unlikely to be with us then 

). First her argument was flight cost (we offered to pay), then it was a 3 day trip was "hard and unfair on bil" (i do this for work 4 x per quarter its fine) then it was he doesnt know his schedule/ term dates (he still won't know this even if we move the date), then it was he has a lot of life changes and its unsettling for BIL. 
Fiance basically just called her out and said she needed to think about her (other) son for a change. He is normally very easy going but was livid about this.
All parties left the call upset including me.
backstory: she is generally a nice lady but being very honest, has some form for drama/jealousy
as well as favoring BIL which irritates me! (e.g. she has various bil/mil only selfies as her phone screen saver, fb profile and whats app profile pic!)
My fiance is really struggling with his fathers illness, alongside a new job and the wedding.
I just dont understand why she is doing this?
I just want us all to have a nice time and cherish the time together while we can.
Help!