From brep to smooth subdivision

Hello everyone.
I am developing a definition that allows me to design aircraft in a totally parametric way. Having obtained the surfaces (fuselage with subd, tail planes and wings with loft surfaces) I would like to create a single surface that softly brings them all together.
I did some experiments, but the result is not appreciable because I get a subd surface that has no symmetry with respect to the xz plane and the trailing edge does not remain sharp.
Can anyone help me out or can you give me a workaround to get a wing karman automatically and with dignity?