I've a nasty feeling it may be correct - I found this on line:
As a fundamental principle, it should be noted that statutory or testamentary beneficiaries directly and automatically obtain full joint ownership of the estate at the time of death of the deceased or testator. The beneficiaries �inherit� all rights and obligations of the deceased.
A beneficiary can waive his or her claim to the estate within a period of six weeks after he or she becomes aware of the inheritance. This period is extended to six months, if the deceased�s last place of residence was, or the beneficiary�s residence is outside Germany.
It does look as though it is possible to waive a claim - and liability???
The German Embassy in London would be able to help on what the law actually is. It's very easy to read meanings that aren't there. Their website has a form to disclaim the estate if that's what is necessary.
http://www.german-embassy.org.uk/inheritance_l aw.html
(scroll down - it's in English as well)