My Sonar Cloud organization is bound to my company’s Bitbucket account, but I can’t add anybody from my Bitbucket account to Sonar Cloud. In fact, it shows me a list of people I’ve never heard of before. They are not any people in my organization - I have no idea who these people are.
Do the members you are looking for already have an account on SonarCloud? This is a pre-requisite to find them and to add them in your SonarCloud organization.
The people you see in the Search drop down are all the users on SonarCloud.