will it affect my Study Permit or my stepsister's PR status if we did not disclose each other's relationship as stepsisters? If I request a record update using the web form, will the IRCC retract my permit and her PR status?
You will be fine. I know a girl that has a half brother and she refused to include him whatsoever. He wanted to include her and did. Neither than were affected negatively by the situation. In my particular case I have three Canadian siblings. I had to tell express entry that they existed. I didn't want to use the points I got for then so I wrote a letter indicating that i'm not close to them. It did not affect my application in any way.