I am in the process of writing a cover letter for a PhD application. The two supervisors of the project are part of my faculty (where I am doing a postgraduate degree), and I have previously been in touch with them through an interview and because one of them taught me some classes last year. I would surely want to address the letter to their names, I am whoever doubting how to officially address them since the first supervisor has a title of professor and the second supervisor has a title of doctor. Maybe having this kind of issue seems exaggerated to some, but I do not know whether to make a distinction in their titles in my letter. I am studying in the UK now, but I previously studied in the Netherlands and getting the right title was always a big issue. To those who might know within the context, can I simply address them both as Dr. to avoid the whole feeling of pointing out their different levels in the letter?
In all likelihood, nobody will pay much attention to this. But if anyone is going to take offence, I think it is much more likely they will be upset if you haven't given them the correct title than because you're "drawing attention to their different levels". So I would address my letter "Dear Prof. X and Dr Y".