Use IAM roles with least privilege to grant all the teams access. Assign IAM roles to each team with customized IAM policies defining specific permission for Amazon RDS and S3 object access based on team responsibilities.

Enable IAM Identity Center with an Identity Center directory. Create and configure permission sets with granular access to Amazon RDS and Amazon S3. Assign all the teams to groups that have specific access with the permission sets.

Create individual IAM users for each member in all the teams with role-based permissions. Assign the IAM roles with predefined policies for RDS and S3 access to each user based on user needs. Implement IAM Access Analyzer for periodic credential evaluation.

Use AWS Organizations to create separate accounts for each team. Implement cross-account IAM roles with least privilege. Grant specific permission for RDS and S3 access based on team roles and responsibilities.