The deadline is January 1, 2018; for informal marriages there is nothing, flexibility simply has its price, just like renting
I wouldn't sign off on that like that. A joint registration certificate with a joint tax return could also suffice for the concept of family. But couples who built without children after 01/01/18 get left out. There will be no partial benefits.
You don't have to be married in the end, right? Joint custody and a shared address are enough, aren't they? Has the term "marriage" ever been mentioned?
Certainly no one knows this for sure now, but I think that one most likely has to be married. Otherwise, it would escalate even further, and from a Christian social perspective, especially the driving force CSU, the family is marriage with children.
Single parent with child should be enough... only that will probably usually fail financially. Wild marriages could then also be supported. That means BauKINDERgeld and not Baufamiliengeld.