, every bank has agreed on a lien in its terms and conditions. So they are allowed to... but when it comes to the point where the bank would want to use it, it is already too late. Even with two banks, because then you have other worries.
And in Germany, obtaining a title to access accounts at other banks takes about 1 month. So whether that still helps... I don't know.
And whether the bank secures the credit card loan with the property depends on the purpose declaration. But it is unlikely that any bank will go ahead and enforce the land charge because of a 3000 euro overdraft on the checking account and thereby liquidate the entire financing. Before that, there will be a lot of alternative attempts at solutions.
All statements naturally apply only to reasonable, reputable banks; this includes cooperative banks, savings banks, the major German banks, and the common direct banks.