I can't tell which beaches they are although I know Zandvoort is a popular beach destination for locals and tourists although I've never been.
For something a bit different try Wijk ann Zee, I lived there for a few months and it's a nice little village with a nice beach (shame about the nearby steel works). Get the train to Beverwijk where there are 3 coffeeshops, the best being Taffne and Splif (in my opinion) and then a 5 min bus ride to Wijk ann Zee which used to have a very smoker friendly bar but I am not sure if this is still open.
Not a great deal of help here , but i'm sure ive seen a pic like the first 1 somewhere in the TR's , sure someone had made visits to where their dad? had been during WWII , good luck searching .
Sending out the good vibes to those that need them right now
I thought about Scheveningen, Hoek of Holland has some 671s too if I remember correctly, but aren't they a touch far out for a bike tour from Amsterdam.
I have been using that source to plan a 1 week WW11 RV trip through Holland, Belguim, France and Germany....starting at Eban-Emael and ending in Berchtesgaden.
If I don't see you no more in this world, I'll meet you on the next one.
JMH