I don't think dw would publish articles without a reliable source. Also welt.de is the online-presence of "Die Welt" (the world in english), which is a major german newspaper. I would say that it's not known for world-class journalistic results and major breakthrough investigative journalistic pieces, but it's still a reliable, conservative newspaper that does solid journalistic work.
It is. It’s the nationwide conservative quality newspaper in Germany that regularly conducts investigative journalism.
It isn't. It's the big brother of the tabloid 'Bild', from the same publisher, rephrasing typical right-wing populism and fear-mongering for readers who like to think they are intellectuals.