Pursue a German PhD with a Masters from the USA? In December of this year (2020) I'll graduate with an MA in Applied Linguistics from a US university (via distance learning/online). I have been living and working as a full-time teacher at a bilingual school in Germany since 2012 and specialize in bilingual education (English/German) with a focus on the subjects of History and English. After graduating, I would like to pursue a PhD in a related field (linguistics) at a university in Germany with the career intention of conducting research and lecturing/instructing at a university. I have seen a lot of German universities host paid PhD research projects with very interesting topics, which seems like a direction to pursue, but I am not sure if the pay will be enough to support my family. I am the main provider for my wife and son (3 y.o.) and we won't be able to financially handle a huge cut to my current salary (about 4,000 Euro gross/brutto per month). 

As to my questions, I am looking for some advice about the potential career-path. Does it make sense for an American to pursue a German PhD with a BA and MA degree from the US? Financially, would it be possible to continue to support my family while pursuing a PhD in Germany? Is it worth it at my age (35 y.o.) to pursue a PhD? 

If the information helps, I plan on staying in Germany permanently as my wife is German, I do not want to continue teaching at the secondary school level, and I am fluent in German. Any advice or guidance would be greatly appreciated!
You can compute your prospective salary yourself: http://oeffentlicher-dienst.info/c/t/rechner/tv-l/allg?id=tv-l-2020 

Typically, TV-E13 but only 50% or 65% depending who funds your position. Whether that is enough is up to you and your wife. A career at the German university is a high risk gamble, and it take quite a while before you know whether you make it or not. If it does not work out, then you will have invested a lot of time in a career that did not work out.