I have not seen the OVA and do not have acess to any of the episodes. So I can't really help connect the meaning of the titles to theyr episodes.
Those names are in german, and perhaps not very good german.
Fräulein Rose being composed of Fräulein, which is an outdated word for a young or unmarried woman (Wikitionary says the word in now avoided and considered disrespectful and sexist) and the word Rose, which does means rose, meaning something like "Young Lady Rose" or "Young lady of the Rose". Probably meaning Shinku.
Rozenkristall is a result of the word Rose being turned into an adjective for kristall, which means "crystal".
The word would mean "Crystal Rose". Which is the meaning of "Barasuishou".
Ewigkeit means Eternity.
Träumend means Dreaming.
Ouvertüre is Overture, no secrets, as the OVAs are a prequel.
I suggest using google translator for any other german title you find in the series, as it seems to be the theme used by the producers.