Is there a realistic chance that they would end up in power in the Federal Government?

A coalition on the federal level between CDU/CSU (~30%) and the AfD (~20%) could perhaps materialize, although it seems a bit unlikely. Would depend on what happens in the world until the federal election, which is held a year from now. en.wikipedia.org/wiki/Opinion...

Almost certainly 'no'. They need a coalition partner and any party who would entertain this would probably end up losing MPs (defections) and votes. Also, on the national level anything above 20% is very unlikely for AfD anyway. Both, AfD and BSW have a combined voter potential of about 25-28%.