I trained a lot for my hike (Le Puy to Sanitago) and got corns. Mine were on my second smallest toes on the inside facing the pinky toes. (My pinky toes are slightly tilted inward, causing rubbing.)
My main solution was corn pads. Sounds like that's not working or you. But just to make sure we're talking about the same things... the pads need to have holes in them so there is no pressure on the corn. You can add two together (like you mention) but that may add pressure to another toe, so that may cause the other toe to rub.
Those worked okay, but things got bad later in my hike, my pinky toes also got very sore. Not corns exactly, but painful/red/swollen. I took some scissors and sliced a slit in my shoes next to my pinky toe. That, along with the corn pads, did the trick. My toes didn't bother me again (after a day or so of healing).
FWIW... I always buy wide-sized shoes (usually Hokas, but also Altras). I had problems in all of them.
I'm training for my third Camino now. No corns right now, so I'm trying the gel toe covers (
link to Amazon here). So far no corns or soreness, but I haven't started the long distances yet. I'm not sure these would help if the corns are already in place, but you might want to give them a try anyway. I'm expecting I'll have to cut my shoes again on the next Camino, we'll see.
While in France and Spain, you'll find a lot of foot care products in the Farmacia, but not always corn pads. I ended up by a rectangle pad they sold (about 6 inches by 4 inches), and would make my own pads with scissors (including a hole to relieve pressure on corn). That worked a little better than the normal pads, because pad had good adhesive and strong padding.
I'm not sure I've provided much help, but maybe something I wrote will help.
Good luck and Buon Camino.
P.S. Post an update here after your Camino and tell us how it went.
P.P.S. I went to a podiatrist about a month ago, before I started my training again, and told him about my issues. He suggested the gel toe covers that I mentioned above, but didn't have any fix other than surgery to correct the positioning of my pinky toes. (He wasn't recommending surgery, just saying that other than wide shoes and padding, there wasn't a ton for him to do for my particular problem.)