going to be making some assumptions here and some facts: firstly No nothing between Miller and Rosenberg just a long standing family relationship as witnessed here http://www.mangago.me/read-manga/datenshi_ni_sasageru_uta_dj_family_visit/an/datenshi-ni-sasageru-uta-dj-family-visit-chapter-1.html/7/ : secondly i assume both Hans and Kurt are in their mid to late teens to be more specific i would assume 17-18 judging by the fact Kurt just graduated and the average age for graduating the type f school he went too i hope my answers helped you in some way
I wonder if Rosenburg and the long suffering Miller ever had a intimate relationship before the young Hans came along. I think that Miller cares about his Colonel more then a professional level.
Also how old is Hans and Kurt?Roseburg mention that they of similar age which is what?