A campaign with 1 GM and 2 players is totally feasible. I ran a 3 player campaign last year knowing that not all players could make each session, so most of the time we were playing with just 2. An advantage of small player counts is that you can really explore the relationship between those characters. I'd suggest talking about that upfront during character creation. Figure out who wants to play the claimant and ask questions about why the other character is committed to the claimant's cause. I also would nudge the players to remember that they can muster levies between sorties. Two people against the world can feel impossible but they have the resources to gather mercenaries and supporters. They can even do a flashback to muster before the first sortie.
I didn't record any of my two-player sessions but you can listen to a one-player actual play here: https://www.partyofonepodcast.com/2020/05/21/234-rebel-crown-with-michael-dunn-o...