I Am Writing My First Novel, Based Upon Real Life Events And Characters. How Can I Disguise The Characters?

I am writing my first novel. It is based upon events and people I knew 20 years ago. I believe it is a compelling story. The details are not typical in any way (I think this is what makes it interesting), and the people would immediately recognize themselves and the events. Whenever I try to change something about the character to make it more fictional, the person no longer seems interesting. Any thoughts/suggestions? Thanks.