Here's my shot: since the two lines are parallel, I figured that the middle point should be equidistant from the parallel lines,so using distance formula:-
$ \frac{2x+3y-5}{\sqrt{13}}=\frac{2x+3y-8}{\sqrt{13}}$
I get, $4x+6y-13=0$(considering one equation +ve and other -ve) which seems to be the right answer, but my question is, is there any other standard method to solve this question?
The locus traced by all the midpoints is just the line in the middle: $2x+3y=\frac{13}{2}$ or $4x+6y-13=0$.