Support the Schaumburg-Lippes is a decision for 
Lippe-Detmold, and it is one of two nearly identical decisions for Lippe-Detmold the other being Support The Lippe-Biesterfelds.
Principality of Lippe joined 
Germany in 1871. After the death of Prince Woldemar, Prince Alexander ascended the throne of Lippe. Prince Alexander was mentally ill so, Prince Adolf of Schaumburg family was appointed as regent. After Alexander's death, the Lippe-Detmold family died out; when the Detmold family died out, there was disputes about inheritance. Ultimately, the Biesterfelds won inheritance of Lippe through the imperial court's decision.
Lippe needs to be independent which, certainly isn't easy, and it has to be 1880. Once enacted, you'll gain 10 prestige and the decision Support The Lippe-Biesterfelds will disappear. One can enact any of them as there are no consequences.
Ingame description
The childless death of Woldemar, prince of Lippe-Detmold, in 1895, marked the beginning of a two decade long dispute between two branches of the house of Lippe, the Schaumburgs and the Biesterfelds. By willing the principality to either side, we can prevent the issue from ever arising.