What's the correct way to put more than one name in the possessive? I want to talk about a wedding between Felix and Mareike. Are any of these correct?
If not, what is correct?
The second form is the correct one, and there is no difference whether it's one or more names. You just use the genitive form. Genitive is the possessive case in German.
Felix’ und Mareikes Hochzeit
For names, the genitive form is normally just the standard form with an appended s.
Mareike => Mareikes
Otto => Ottos
Alexander => Alexanders
However, for names ending in s-sounds, namely in s, ss, ß, tz, z or x, the genitive form is instead the standard form with an appended apostrophe.
Felix => Felix’
Marcus => Marcus’
Jens => Jens’
Der Roman „Der Butt” von Günther Grass => Günther Grass’ Roman „Der Butt”
The apostrophe has nothing to do with the one in the English possessive, but stands for the "omitted" genitive ending.
In older German, you might also find the older genitive form ending in -ens, but this not in use any more:
Felixens und Mareikes Hochzeit
In very old texts (as well as in current ones from people who don't care), you may encounter the possessive apostrophe like in English, see this question.
Colloquially, the form with "von" (of) is popular:
Die Hochzeit von Felix und Mareike
(The wedding of Felix and Mareike)
