My Fiancé and I are getting married in December this year. In February, we discussed the pros and cons of having an adults only versus a kids-present wedding. We decided together to have an adults only ceremony and reception. My fiancé has 2 nieces, his brother's children. At the time of the decision he understood our decision means his nieces will not be invited to the ceremony or reception.
Less than 48 hours ago at the time of posting (July), my fiancé's brother decided he wanted to bring his children to our wedding and, in my opinion, has behaved brutishly attempting to force me and my mom, by emotionally abusing my fiance, to change wedding arrangements to accommodate him. He has threatened to cut my fiancé from his life if we do not give in to his bullying and invite his children to our wedding. He thinks it is no big deal to make an exception for his children to attend, but not invite all the nieces and nephews that are excluded on my side due to our decision to have an adults only ceremony/reception.
I would like to tell the brother-in-law where he can stick it, but I love my fiancé, and he wants to try to mend things with his brother. What should I do? I do not want such a toxic person anywhere near our joyful day, to say nothing of having him near my future with my fiancé as husband and wife.
Advice or ideas on how to deal with this nightmare in-law in the context of our wedding is greatly appreciated. I am at my wit's end.