This is something lovely you've conjured here, a whole new canon of magic and of language. I've never been convinced before by the various efforts at articulating spells for mpreg/fpreg. But the image you wove here, of a tangible life force visible in the wand, summoned and driven by Narcissa's voice, really worked for me. I could accept the mechanics of the conception and also the realness of Narcissa's equal (bio) parenthood.