Etiquette between Reigning/Sovereign Houses and Mediatized Houses

[Eutropius]

I was wondering if anyone had any knowledge about etiquette rules in Germany (prior to 1918) surrounding relations between mediatized and sovereign/reigning houses.  For example: Would the wife of a mediatized prince be expected to curtsey before a prince/princess of a reigning family?   Another example: If two princes from reigning and mediatized families were friends, would the mediatized prince have been expected to use the German formal form of "you" - Sie - when speaking to the prince from the reigning family?  Just curious...