Jean,
That sounds great, Ihope you'll find a window to come!
And I imagine the ambassador's face when you ask him which sweets he suggests for german nuns 
If you ask me I would recommend the peppermint patties sound good, peanut butter is not every one's cup of tea in Germany and Snickers, Milka and the rest can be bought in every supermarket.
If your dad knew that the Ludendorff bridge was under american control and also the direction to Remagen, they could find the way cross-country quiet easy. It's a way of about 20 km bee-line, not so much in peace but in war-times... They would have passed the Siebengebirge ("Seven mountains", but a trained person can climb them all in one day), and these mountains can be seen from the Michaelsberg so theyhad a landmark for their orientation - but if they were hiding in a farm I assume that they have not reached the mountains. After leaving the city of Siegburg most of the way was untilled at that time. There were heavy battles in the Siebengebirge, but on 21 March the area was under american control. I have ordered a book about the last days of the war in this area, I hope we'll find some information about the american units in the area. I have googled a bit, but it seems as if hundreds of escaped prisoners of all nations were hiding in farms at that time all over Europe, and there have been hundreds of (also forced) labourers in the area between Siegburg and the Siebengebirge, many of them working for the farms, and many also from Belgium.
Christoph