Create Guidelines for Loft across 3 axis

I have two pairs of lines. Each set moves across 2 axis and i was attempting to use them for a Loft as guidelines, however, the loft produces the wrong shape due to the one pair at the bottom not following the same curvature as the other pair.

How can i combine my curves to produce a guideline that will achieve the correct loft guideline?
Another way to ask the same question, how can i generate a line which curves in 3 axis at the same time?
More pictures so you can see what was desired vs what i had to compromise with. The compromise, if not obvious, was to ignore the lines that didnt curve up and down and only use 1 pair as the guidelines for the loft.