I'm going to refuse to be a sperm donor for my sister's wife
Is your sister's wife the reason for your reticence?
Yes. I hate her and it's my way of getting revenge.
You have full decision making authority on where your sperm goes in this situation, but if you don't want to because you hate your sister's wife, this is not correct. Hate is a bad motivation.
I just want to screw with her and make this situation a mess for everyone else.
Your sister's wife is your family and she and your sister care for you. Hating your sister's wife is not right and not helping her is wrong when driven by this hatred. Let your animosity go and support her and your sister.