The point hasn't yet been made with regard to the ear-witness's comments and the photograph taken immediately post-crash.
If there is the impression that the engine was running after separation and that the horizontal vapour is evidence of this, I think that is incorrect.
I think given the deformation of engine casing/cowling and rapid exhaustion of fuel in what remained with the engine of the severed fuel line, neither engine "continued to run" after impact.
On the contrary, the engine with less cowling material attached shows distinct evidence of rotation which was stopped quickly by impact damage, (many blades bent back opposite direction of rotation, some straight blades remaining).
Although there is some backward-bending of the blades seen, it is difficult to say more about the other engine as the view in the photograph of the blades is more obscured.