ANSWER:

You have the option to either please Allah or please them!

You must not attend a wedding or any gathering where there’s free mixing or music or any other haram activities. They are not paying any attention to your request of segregating it, why should care for their feelings? 

There’s no obedience to the created at the cost of disobedience to the Creator. 

My paternal cousin sister is getting married and is stubbornly insisting that I attend. I refused as it will be mixed but she started crying and her father (my uncle) said he will break ties with us and will withdraw from any of my life events if I don’t go. What should I do?