Thought this was amusing... in Germany as I think is the case here one can take both last names of the surname... but not if one of the surnames already includes two last names. Given the exponential nature at which last names could grow... probably a wise move.
German triple-barrelled ban holds

Germany's highest court has upheld a law which makes it illegal for anyone to use more than two last names.

A married couple challenged the 1993 law after they were forbidden from joining their surnames - one of which is already a double-barrelled name.

Frieda Rosemarie Thalheim married Hans-Peter Kunz-Hallstein in 1997 but both had wanted to retain their surnames.

The court ruled surnames made of three or more different names made it more difficult to trace back a family line.

After the ruling, Hans-Peter Kunz-Hallstein told the BBC he and his wife were disappointed.

"We're married," he said, "and we want to show it."
BBC NEWS | Europe | German triple-barrelled ban holds