You seem to be assuming that just because they’ve found a hiding place, they won’t be discovered. That seems overly optimistic. Think of Saddam Hussien in the spider bunker, think of Anne Frank’s family.
I think they’d seen / heard enough about the atrocities being committed around them to understand perfectly that they would most likely be discovered, and when found, likely face violent torture/rape/beating/maiming before being killed.
It’s the choice between suicide with some dignity and (hopefully) minimal pain and capricious murder. Paul was saying to his wife, “You and the kids must take your own lives.”
In the movie, he found them in the hotel room hiding in the shower. If anyone had been intent on killing everyone in the hotel they would have been found and killed. As it happened, in this dramatic recreation of events, they lived another day. But this isn’t to say that ever really occured, or that Paul’s decison wasn’t a more realistic reaction when you’re living under siege, and ultimately an act of love.