I don't want my step sister and her bikie fiance at my wedding
Why don't you want her at your wedding?
She's a cunt. That's all I have to say about her.
While I can understand not getting along with someone, think carefully before you exclude your sister from your wedding. That is something that will harm your relationship with her, perhaps permanently.
I still don't care.
If you really have a problem with her you should try to work it out before the wedding. If the whole thing is because you are racist against her fiance that is pretty mean. You can let them have a good time and mind your own business, and party with your other guests.