I'm going to ghost the couple I had a threesome with
Why are you ghosting them? Do you not want to see them again?
I am never going to have contact with them again.
Having casual sex with people does not mean you have to have a relationship with them. You have a right to privacy and move on with your life.
I am doing this to avoid being bothered.
It sounds like you are making the right decision for yourself. If this started as casual, they may not try to contact you again anyway.