Two star-crossed lovers, one a wizard, and one a witch, fight to stay together while both of their families engage in a neverending war.

Another angle:
"Two star-crossed members of feuding witchcraft and wizardry families fall into a forbidden love."

I can see something like this:

With their families' being mortal enemies, two star-crossed lovers, a wizard, and a witch must ignore the rules and stay together.

I hope this helps