That could be their plan, but if we don't remove the barricade, we're stuck in a standoff.
Channeling Sun Tzu...
1. They stop the train and order their men to pick off anyone working on the barricades.
2. This means the train will respond with a direct attack to try and free the train.
3. Having diverted the trains defenders, a 2nd force of Bandits invades the train.
4. They take control of the train. At this point they can drive it away if the passengers have cleared the tracks (this is probably their idea), or flank the people attacking the hill.
Ideas
~The forces attacking the Hill just have to sit tight and defend. Anyone attacking them is people not defending the train. I think they would be the less experienced bandits, and would consequently be less nimble to adapt.
~So I think they'll also stop firing at the barricade as soon as someone attacks the Hill. Because while they want to encourage an attack to draw off defenders, but they definitely want people doing their work for them so they can made a speedy escape. Otherwise they're stuck along with the people invading the train. I believe the idea is they get the train and everybody runs away.
~The train attackers likely, will wait for the defenders to attack the hill AND for the work on the tracks to begin in earnest.
My idea is a feint attack on the Hill to trigger phase 3 of their plan. Just a short skirmish to clear the barricades as quickly as possible-the men should hit and run. We want to clear the tracks and flee before Phase 3 gets done-could maybe have some sort of signal to get everyone back.
TLDR Engaging the hill bandits in earnest seems a disastrous tactical blunder. They're not a dire threat to us up there. They can kill people, but can't take the train. We only need to distract them long enough to free the tracks, and I'm pretty sure Fiona can encourage it to be done quicker than the bandits would reckon. If they have another group waiting, it'll be the main threat.