Choosing the right part of the Camino

Would they like to ride through Poo?

Hi Maxi
There aren't many bicigrinos on the forum, which is probably why you haven't had many responses yet. But I'm sure they'll free-wheel along eventually...
As a walker I'd say there's a practical issue here - much of this section of coast carries a major national route, and also sometimes an autoroute, pressed quite close to the actual coast, by the adjacent hills. As a walker you sometimes go off and on the national route, but then also have the option to take small coastal paths in between. Most of these aren't suitable for road cyclists, so in these situations you would have to negotiate the main roads. However the is one very pretty section where the hills have receded and the main road goes further away from the coast, and this is what I recommend... the camino from Laredo to Santander. It is relatively flat and the road cycling will be on small quiet roads. This has the added adventure of two trips on ferry boats (to Santona and to Santander) some fabulous beaches and also lovely cliffs on the coastal option from Guemes. Guemes is one of the most famous albergues on the Norte and I feel sure you'd all get a warm welcome there.
I recommend you have a look at Mapy.cz (select outdoor map option to see the camino) and also Gronze for these two stages.

If you don't mind hills, if you go east along the coast from Bilbao the scenery is stunning, but the climbs just as much.
The roads are pretty quiet and motorists expect to see cyclists on it.
The Basque country is very very hilly and challenging for a cyclist.
I can't comment on following the camino towards Gijon