Do Apapa and Amama actually mean 'grandpa' and 'grandma' in Russian (or Danish, or anything else) or were those terms pet names invented and used exclusively by the imperial family?
To my knowledge only babushka and dedushka mean 'grandfather' and 'grandmother,' in Russian, but I'm not fluent enough to know whether or not Apapa and Amama might be equivalent to American colloquialisms like nana, poppa, gram, and gramps.
These terms come from King Christian IX and Queen Louise of Denmark. I don't know if they are Danish in origin, but Constantine II of Greece acknowledged that out of tradition, his grandchildren refer to him and Queen Anne-Marie as "Apapa" and "Amama".
As a a Norwegian with a fairly good knowledge of the closely related Danish language, I can say that Apapa and Amama are not normal Danish terms for grandfather and grandmother. The usual Danish terms are
farfar (paternal grandfather),
farmor (paternal grandmother),
morfar (maternal grandfather) and
mormor (maternal grandmother). Apapa and Amama are children's renderings of
papa and
mama, the not very usual forms for "dad" and "mom", as far as I can tell in Denmark mostly limited to the higher classes (upper bourgeoisie and aristocracy), as they are foreign, derived from German (
Papa and
Mama) and ultimately from French (
papa and
maman). In TV Interviews, the present Queen Margrethe refers to her father Frederik IX as
far, father/dad, and her mother Queen Ingrid as
mor, mother/mom, like most Danes.
Apapa and Amama are what Christian IX and Queen Louise's children called their parents; and their children (i.e. the grandchildren) continued the usage - for their grandparents.
