I finally figured out that the subject is so fraught, with such a tough history of discrimination, no word, even if well-intentioned, is going to heal up the hurt.
Until our culture changes to be truly inclusive--with no more "What are you?" as an automatic introductory question--we will not find the perfect word to describe a complicated history. But until then, we humbly do our best as our language evolves, trying to catch up with the ever-changing reality of families whose members, defying social norms, come from historically separated groups. Families whose members, no matter how different they may look to outsiders, love each other.