a) You will need UiPath Automation Developer licenses for this. Normally, you will also have Attended User with it due to the capability is included.
b) 10 Attended User licenses. during installation, you will use the same installer as the UiPath Studio. However, you can choose to not install UiPath studio when during the installation process.
For further restrictions, you can use UiPath automation ops to be able to further segregate the roles and functionalities of each user.
Attended - Named User : To simply put, this is the attended Robot. UiPath recently changed the naming of licenses. Hence, if you are looking for attended robot, you can refer to it as attended User
Citizen developer: This license has the Studio X Profile, take note, you wont have access to UiPath studio profile with this license. This also has attended user for running the tasks that are created.
RPA Developer: This is a deprecated license. This is not available anymore. RPA developer license means is a devellopment license which includes UiPath Studio and Citizen Developer Profile. This has been replaced by the Automation developer License. Take note this does not include Studio Pro, meaning, no test automation capabilities
Automation Developer: The latest sku for development. Includes Studio and Citizen developer profiles. In this license, Studio and Studio Pro have been merged. Hence, you wont see Studio Pro but this will have the testing capabilities.
I hope this clarifies. Let me know if there are any issues