So this is the route my brother is recommending (it'll take you about 10 minutes more than the route you printed) : 
Time: 4 hr 45 min
0.0
Start: Head southeast on Rue du Président Wilson toward Rue de la Marine
0.1
Turn left to stay on Rue du Président Wilson
0.1
Turn left onto Bd Alexandre III
0.3
Turn right onto Pl. Jean Bart
0.3
Continue onto Bd Sainte-Barbe
0.8
Turn right onto Av. du Stade
Go through 1 roundabout
1.1
Continue onto Av. de la Libération/D635
Continue to follow D635
1.9
Keep left at the fork, follow signs for A16/E40/Ostende/Bruges/Bray-Dunes/Furnes/Veurne/Téteghem and merge onto A16/E40
Entering Belgium
9.9
Continue onto E40
92.5
Take exit 11-17-Groot-Bijgaarden for E40/E19 toward E411/Namen/Luik/Antwerpen/Luchthaven Zaventem
93.3
Merge onto E19
93.9
Continue onto E40
101.4
Slight left to stay on E40
104.3
Slight right to stay on E40 (signs for Luik/Leuven/Brussel)
183.0
continue on E40 (signs for Köln)
take exit 4 (Kreuz Aachen) to stay on E40 and continue following signs for Köln
Take exit 9-Kreuz Kerpen to merge onto A61 toward Koblenz
228.0
Slight left to stay on A61
264.8
Take exit 34-Mendig toward Mayen/Maria Laach
264.9
Turn left onto B262
270.0
Slight right onto the ramp to Trier Koblenz/Münstermaifeld/Mayen-Süd-zentrum/Mayen-Süd-Alzheim/A48
270.1
Keep left at the fork and merge onto B262
272.4
Merge onto A48 via the ramp to Trier
288.7
Take exit 2-Ulmen toward B259
288.9
Turn left onto B257
289.2
Continue onto B259
291.2
Turn right onto L102
291.7
Turn left onto Kirchstraße
291.7
Turn left onto Brunnenstraße
291.8
Take the 1st right onto Talstraße
Destination will be on the right
291.8
Arrive at Auderath, Germany
And in case you lot want to make a break, my brother said it's best to do it after you have passed Brussel. Try to get past Brussel by noon, otherwise that bit will be manic. Well, the whole route could be manic anyway because that Friday when you come over is when everyone travels home for a long weekend.