I only have a recumbent trike but ...........
The skittish steering sound like a headset bearing issue.
I've never had over twitchy steering on my ICE trike even with the headsets a fraction loose.
But if I overtighten my headsets then the steering feels notched and it starts to hunt for a line on corners.
How are the front brakes set up ??
When I ran twin cable disks off a single lever, I found it very fiddly to get them both working at the same stopping power over the full lever pull.
I found it best if it pulled slightly under light brakes but straight under heavy braking.
As for steering into the ditch off a camber, that's just classic trike behaviour .....
If your arms aren't relaxed then when you lean right to counteract the camber, your hands move slightly.
Also on a trike if you lean right then the trike will naturally try to go left.
Both these effects together starts to steer you into the ditch.
The more you go towards the ditch, the more you tense up and it just gets worse.
If you stiffen your left arm and relax your right it will both hold you up against the camber while keeping the trike straight.
On a trike you first steer then lean.