Formal:
* Mes sœurs s'appellent... (My sisters are called...)
* This is the most formal and neutral way to say it.
Informal:
* Mes sœurs s'appellent... (My sisters are called...)
* On appelle mes sœurs... (My sisters are called...)
* Mes sœurs, c'est... (My sisters are...)
With specific names:
* Mes sœurs s'appellent [Name 1] et [Name 2]. (My sisters are called [Name 1] and [Name 2].)
* Je m'appelle [Your name], et mes sœurs s'appellent [Name 1] et [Name 2]. (My name is [Your name], and my sisters are called [Name 1] and [Name 2].)
You can choose the option that best fits the situation and your level of formality.