No. They tap your link and answer in a browser. No app, no account, no password.
No. Answers go only to the planner. Nobody invited can see anyone else's answer — not even whether someone else has replied.
On the thank-you screen after you answer, there's a personal edit link — copy or bookmark it and you can change your answer any time. If that's gone too, your answer is still safe: just ask the planner for the invite link and answer again. They can merge your answers on their end, so nothing's lost.
Everything about an event auto-deletes about 30 days after its last proposed date.
Open Settings in the app and tap Delete account. It erases all of your events and everyone's answers, and signs you out of SheduleIt with Apple.
Email support@youinoroutapp.com and a human will read it.