Children of the Wandering House

On a planet called Oikos—where tree Houses are gods who make families: once a man and a woman marry, a House chooses them, and, eventually, babies start emerging from the literal woodwork. It's an intriguing life until the heroine, Berry, is stranded by her House when giant moths show up one night, killing Houses and wreaking havoc, in concert with an unwelcome visitor from another world who plans to exploit House resources.