Hi @pixelgra
Members provides capabilities provided by WordPress platform, theme, or one of the plugins installed on website. It does not provide any other capabilities. When it comes to managing images in Media library, WordPress provides Upload Files capability available under Media tab of Edit Role screen.
When it comes to capabilities provided by other plugins, like Sendinblue, plugin authors can use any capability they want, including custom capabilities to access their features. If you know which capabilities are required to manage Sendinblue settings (you could reach out to their support to see if they have special capability), you can assign those capabilities to a user/role.
Best