I'm surprised that her husband allowed them inside in the first place.
EDIT: Has the point been reached where people are more afraid of being mis-targeted (e.g. my Chinese gf has a pressure cooker for rice) than being an actual "terrorist" attack victim? I sure hope so.
(If there is a number of guys with guns at my front door I'd probably have to let them in..)
Reading the warrant will give you some indication of what they're interested in. If they don't have a warrant, then you can decide if you think you should let them in.
It's up to you; if I'm on a jury, I won't find you more suspicious if you question the police before allowing them into your home. I'd guess that there are other people like me.
We just don't have that much police and secret services poking around in our private lives (yet), so let's see what I'll do when I actually come into the situation. :)
[0] https://en.wikipedia.org/wiki/Berlin_population_statistics#P...