Bmesh how to make faces

i did the countour of 2 shapes like shown in pic with bmesh

but would like to be able somehow to give it some 3D curve rounded if possible

i can add an Ngon face but that wont help to shape it as a 3D surface!
like a sea shell coquille st Jacques

for the bottom shape i did only 1/2 of it not this whole over crossing faces !

i can see now that this is symetrical Y axis
so i’ll redo the equations
so that it can do 1/2 the object with the 2 curves at same time and try to make quad faces
but this wont give me loops then how to extrude middle may be with proportionel edit to give it 3D shape as a coquille st -Jacques?