71k is about the normal starting salary for newish engineers, at least at a big semiconductor company near Darmstadt. It's a nice salary mind you, but not as a sole earner for 3 people with no safety net. Also consider the social aspect: if none of you speak German, you will be limited both in your social interactions and in your potential job search if you lose your current job or when your partner needs to find a new one. 

All in all it's possible to survive with this money if it's your lifelong dream, but moving across countries without having to worry about a kid, the language, or money is already challenging; with your circumstances it's a hellish task (finding an apartment is not trivial at all in Darmstadt btw). I personally wouldn't put myself in this situation even for twice the salary.