I typed a long reply last night but it doesn´t seem to be here! Hopefully I can remember the gist of it.
That photo… just to be clear it´s not a great place to ride. A fall could be fatal there, it´s way more exposed than it looks. The coast there isn´t great for biking either. It´s a really cool spot and I went to watch the sun set. Anyone who does go there with a bike should remember it´s not really what it´s for, it´s a church, so you need mucho respecto!
If you´d like to drop me a mail I´ll see if I can help. It´s not that easy because there aren´t marked paths round us so you end up mixing and matching paths. A lot of the stuff is linked in with trails local people have built or cleared themselves which aren´t on maps. One easy thing to do is follow the coastline, it´s hard to get lost if you keep the sea to one side. You can do that all along the coastline and have a good day out. Be careful because some places it´s not allowed, and the French are really militant about enforcing that.
If you´d like guiding we can often make a private group for a family. I think from reading your mail you probably are looking to snatch a few hours on the bike rather than days out though. In that case Coastline is good! Or try Irrisarri Land, it´s like a mini BPW I think (never been to BPW) and good fun for a few hours.