HTML Code > Cloud Page > Single selection checkbox and textbox for 'others'

I want to write two separate rules for a checkbox survey question on a Cloud Page:

• A rule to make sure that people select only one option. They can't choose multiple options
• I want to have the last option as 'Others, please specify' and include a textbox for them to fill in

Current code in SFMC Cloud page

I'm not sure how to proceed with either of these rules, so could use some recommendations.