This paper sets out to show how a trilingual teaching sequence delivered primarily in minority L2 Basque can foster not just development of oral presentation skills in Basque, but also in L1 Spanish and L3 English. We set out to show that such a trilingual teaching intervention, based on the principles of integrated teaching of languages and translanguaging, can effectively promote multilingual skills in the Basque educational context. The teaching sequence involved alternation between the three languages, but Basque -- the minority language in this case -- was the language given preference. Oral presentations produced by the 16-year-old trilingual students before and after the teaching intervention were evaluated for key elements. Our results generally showed development in students' oral presentation skills on our key criteria, not only in Basque, but also in Spanish and English. We conclude that carefully planned language alternation and an integration of languages within a genre-focused teaching sequence can offer an effective teaching approach for Basque immersion education, promoting multilingual development including the minority language.