You could use the Birail3+ tool. Here is a VERY quick example using your original curves.

1. I made the rail curves planar
2. I used the ep curve tool to add some profiles
3. I cut the rail curves where the first and last profile curves intersect (note you would build the end bits using boundary surfaces)
4. I created the surfaces using three separate birail operations as I got odd shapes trying to birail the surface in one shot
5. I rebuilt the surfaces in (u,v) = (6,4) and attached them and tweaked the hulls and control point just a little.

Far more tweaking needs to be done but this is a good starting point for 5 minutes of work