lines between 3 curves

Hi

This is propably a very simple thing to do but since I am new its not simple to me.

I have three curves (not planar) between which I want to place two lines that in plane make a 90 degree angle.

I have placed the first two lines and the points at the mid curves where the rest of the lines should be placed. My problem is to divide the two outer curves at the right length.

rhino.jpg