Which solution will meet these requirements while complying with the principle of least privilege?

Explanations:

Attaching the Administrator Access policy to the development account users would grant them full access to all resources in the account, violating the principle of least privilege. This is not a secure practice, especially in a production environment.

Adding the development account as a principal in the trust policy of the role in the production account allows IAM users in the development account to assume the role and access the S3 bucket in the production account. This adheres to the principle of least privilege by granting only the necessary permissions for specific resources.

Turning off the S3 Block Public Access feature would expose the S3 bucket to potential public access, which is a security risk. It does not align with least privilege practices and does not address the requirement of providing controlled access to the bucket.

Creating a user in the production account with unique credentials for each team member adds unnecessary complexity and management overhead. It also does not facilitate access for existing IAM users in the development account, which is the requirement. This option does not align with the principle of least privilege as it creates more users than necessary.