First of all, thank you for the response! I'm very glad to hear that their driving is good

Another question: we are coming from Aachen, going via Köln - Hessen - Erfurt, arrive in Leipzig. We hope to pass Aachen at around 6 o'clock, considering it's a saturday, but during the holidays, should we expect lots of traffic?

Second question: I have driven in Germany before, and I think I'm familiar with the German speed limit system: if you pass an Anfarht (an Autobahn entrance) and there is no sign indicating a speed limit, there is no speed limit, is this true? This is what I was told by a German acquaintance. Before this, I only went above 130 km/h if there was the white sign with thin black lines. Which one is correct?

Third question: are there many stretches of road on this route where there is no speed limit?