So it should be
... ihrer Sozialgeldern
isn't it?
No, it shouldn't and it isn't.
German Komposita (composite nouns) always retain the declination of their last part. "Sozialgeld" is built from two words: "sozial" ("social"), which is an Adjektiv/Adverb and "Geld" ("money", sometimes also "funds"), which is a Nomen (noun). So, the way "Sozialgeld" is declinated is like "Geld" is declinated. "Geld" is a bit irregular, here is a table:
das Geld (Nominativ singular)
des Geldes (Genitiv singular)
dem Geld (Dativ singular)
das Geld (Akkusativ singular)
die Gelder (Nominativ plural)
der Gelder (Genitiv plural)
den Geldern (Dativ plural)
die Gelder (Akkusativ plural)
Now we have to find out which case is used:
(Allerdings 1) (müssen 2) (sie 3) (zwischen ein und zwei Prozent ihrer Sozialgelder 4) (für 5) (die Leistungen der Krankenkasse 6) (abgeben 2a).
Nevertheless they have to give up between 1 and 2 percent of their social funds(?) for the services of their social security (provider).
- is the so-called Vorfeld, it translates to "nevertheless"
- and 2a) is the Prädikat, the Verb "abgeben" along with the Modalverb "müssen" - have to ... give up.
- is the subject of the sentence, "they"
- This is the interesting part. It is an Objekt in Akkusativ (they have to give up something) but consisting of the "core" object itself ("1 or 2 percent") and an Objekt of this Objekt, so to say. This "sub-object" is in Genitiv, the most common analogon to the english possessive: "ihrer Sozialgelder".
- introduces another Objekt, "for"
- is this other Objekt, also in Akkusativ and constructed the same way as 4: a main part in Akkusativ ("die Leistungen", the services) and a sub-part in Genitiv ("der Krankenkasse", "of the social security provider").