Through in-home ethnographic observations of three multilingual immigrant families' shared book reading, we identified recurring literacy practices in the home in which mothers, older siblings, and younger children participated during the reading. We found that families engaged in context-sensitive and cooperative shared reading practices, wherein decoding tended to be the focus. This practice--which we call transcultural decoding--involved multidirectional language socialization practices and occurred across languages, and older family members contributed both expertise and restrictive conceptions of reading. This work suggests the importance of (a) acknowledging the major focus on decoding during shared reading in families, and reconceptualizing that work as complex and nuanced, particularly across languages and cultures, and (b) considering siblings as cultural and linguistic mediators in family literacy practices.