This article analyzes how couples made up of two mothers redefine their roles when they break up as well as how legal professionals frame the custodial arrangements of these former same-sex couples. To do so, we focus on the case of Quebec, Canada, where parentage equality between mothers was attained as early as in 2002. We rely on individual semi-structured interviews with mothers’ (N = 17) and legal professionals’ accounts (N = 23) as well as on court records regarding physical custody arrangements. We find that the legal recognition of both mothers favors coparenting practices, and especially joint physical custody. However, the heteronormative frame of custody arrangements lingers. Sexual minority mothers struggle with the valorization of birth motherhood and with the standard of gendered parental complementarity. Indeed, professionals can still fall back on heteronormative norms, notably by assigning to non-birth mothers a “paternal” role. In the end, the inexperience of many professionals on LGBTQ+ issues, the embeddedness of heteronormativity in day-to-day relations, as well as the permanence of heteronormative legal categories and professional practices are all factors that set these families apart.