How marvellous to had a dad/son walk on the Camino!!!! Sure, you will see staffs at many shops but you cannot guarantee when and where ... unless you have time in Pamplona to look around before you start. If you arrive by bus there is a shop in the bus station, Azular, which sells books and guides and "things Camino" and I am fairly sure I saw staffs there last April - though I may be wrong (I often am).
Rather than taking a taxi anywhere you could stroll out the easy 5 kms to Cizur Menur and stay at the very pleasant and comfortable Albergue Peregrinos Maribel Roncal.
The descent from the Alto de Perdon is as it has always been ... boulders, loose - but don't be put off as it is a marvellous descent, utterly beautiful. The only place on the planet I have walked upon where I wouldn't have been surprised to see dinosaurs! Don't be put off by the scare mongerers, the fearful, as it is perfectly safe on the one condition that you go slowly. If you don't go slowly you will find yourself speeding up and may take a tumble - slow and sure does it.
However, if your heart fails you you can take the small tarmac road to the right from the top and turn left at the bottom and left again and you will end up in the same village you would have arrived at, Uterga. Adds a couple of kms but is good tarmac all the way and not steep.
Uterga has refugios, as does Muruzabel .... so you don't have to worry about doing great distances - in fact, lose that now - you don't have to walk exhausting distances on any day ... the guide books are exactly that, guide books, not rule books - so walk the distances that you want to walk and stop when tired ... is a lovely section your son has chosen, with plenty of refugios - none of which will be very busy - and places to eat all along the way ... so be relaxed - enjoy!!
Keep an eye on the weather before you go - this is a good site to do that -
https://www.accuweather.com/
Buen Camino!!