Just need Sakura Chiyono O (Maruzensky's 'son'). And Buena Vista (Maruzensky's other 'great-granddaughter', also Special Week's 'daughter').
Though think those two weren't implemented yet when this art was drawn.
Anyway, if you carefully notice, one of them is based on a RL mare while the rest were stallions. This is actually alluded to in the art and character design.
The eardecs. Or hat/hairdecs in some cases.
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Real-life horse is the grandson of Maruzensky.Real-life horse is the grandson of Maruzensky.Real-life horse is the grandson of Maruzensky.Real-life horse is the great-granddaughter of Maruzensky.Real-life horse is the ancestor of the RL equivalents of all the other girls.