So - here is my humble suggestion:
This place will take 2 hours and 11 minutes to get to for you Rob, and 2 hours and 18 minutes for us (from Calais). Which means that we would arrive by 14:15 at the latest (we leave Calais at 11:55), not including breakdowns. The only drawback is that 27 minutes of this journey we will be on the same piece of road before meeting up, but I can't see anywhere nearer Brussels that is as easy to park, and as interesting. This is on the way to our ultimate destiation too (we drive this way anyway).
This is called "The Kouterhof" in the village of Hoegaarden - it is part of the (working) brewery there, and serves a variety of easy-to-eat food, as well as beer!
Brewery website: http://www.twitgebrouw.be/
Cafe/restaurant website (sort-of in English): http://www.kouterhof.be/documents/home.xml?lang=en
Here are directions: http://www.twitgebrouw.be/_pdf/en/PDF-Info.pdf
I don't think we'd need to book (you will have to translate Rob!), and I can't think it would be that busy at that sort of time.
From here it is 2 hours to Luxembourg.




