when the duchess gave birth to medea, it was the day she died. Medea never had the chance to see her biological mother. Hence she had a abusive stepmother who forced her to be 'smart' at young age. Dekis left the solon duchy as soon medea was already grown up.

The two didn't expect to meet their mother's reincarnation-- you. The way you talk the way you act reminds them of their mother. Medea got her mother's appearance so she surely knows it was you at the first place. And..dekis too.