In the Swedish compulsory school system, multilingual students' reading and writing development is supported, among other measures and practices, by heritage language (HL) teachers. To effectively support multilingual students, whether they require special educational assistance or not, collaboration between heritage language teachers and special education needs (SEN) teachers is essential. Thus, a key consideration is how HL and SEN teachers work together to promote reading and writing skills in multilingual children. We present two sub-studies: Study 1, a questionnaire answered by 33 HL teachers, and Study 2, consisting of in-depth interviews with a different group of 13 HL teachers. Both sub-studies aim to increase our understanding of HL teachers' experiences of collaborative practices with SEN teachers for promoting reading and writing development among multilingual students with or without the need of special educational support. The findings reveal that HL teachers, though well qualified and committed, are often excluded from collaborative planning with SEN teachers. This study highlights the systemic barriers and opportunities for improving literacy support through interprofessional collaboration.