There is a lot of hoohaa about the Route Napoleon.
It is not a technically difficult, tough, mountain trail. It is a steady, steep climb for 16km, no downs and very few flat sections, until the end, but neither the first 14km on a tarred road or the last 10 on a path are 'terrible'.
I suppose if you are completely unfit it can be a 'terribly steep stage' but I have taken not-so-fit people on that route and they have all made it and lived to tell their tales! There is a steep down at the end - you have to choose between 6km (road route) or 3km (beech woods).
If you do it in two days it will be a piece of cake. The first 14km or so is on a narrow, tarred road -consistently steep up from St Jean. After 5km you reach Huntto. Stop for a rest and a coffee or coke. At about the 6.4km mark there is a fountain and a table. Stop for a look at the view - if it is a nice day, take photographs!
Another 2+ km and you reach Orisson. Stay for the night. I think it is €32 for a bed and dinner/breakfast. If you don't get in, stay another night in St Jean. Get a taxi to fetch you from Orisson and take you back to St Jean (± €8) and bring you back the next day.
3km beyond Orisson you see the statue of the Virgin of Biakorri on the left. (11km) Stop a while to catch your breath and take photos.
Another 2km further a road joins yours from the right. (This is the road to Arneguy which is on the Val Carlos route. The tarred road ends about 2km further (at the 15km mark) just after the sign that reads Roncesvaux/Orreaga.
From there you are on a lovely, grass path - still going up but not at all scary. It is not a rocky mountain track and there is no difficulty in walking it - its just steep. 1.5km later you come to a wooden sign that directs you to the Col Leopoeder and Roncesvalles.
At the 20.5km sign you have two choices; take the path into the beech woods - VERY steeply downhill for 3.5km through the woods which can be trecherous in wet weather. You might have to go down like a side-winder if it is wet. Or you can opt for the slightly longer road route to the Ibañeta pass where the Val Carlos route joins and down to Roncesvalles.
I've walked both routes - Val Carlos and Napoleon. On the Val Carlos route we stayed in a Casa at Val Carlos and then went over the Ibaneta Pass the next day. The scenery is stunning on both routes. There is a lot of off-road walking on the road route and the last few kms to the pass on the road route are even steeper than the Route Napoleon!
Send your pack ahead to Roncesvalles if you want to and just carry essentials in a daypack - many pilgrims do. They are taken to La Posada and you can collect them there.
Check the weather forecast and base your decision on that. Mind you - even the weather forecast isn't always right!!