AssalamuAlaikum sheikh.
I am a male person. Can I be a tutor of two girl students(non maharam) along with my own sister? So as the number of total students is 3 and the girls are in hijab together then will I be sinful for teaching them?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If there is a female tutor to teach them, then it would be preferable and more prudent in terms of clearing your liability from sin and avoiding falling into Fitnah (temptation). If there is no female tutor to assume this role and there is a need to teach them, then there is nothing wrong with that – Allah willing – as long as there is no fear of Fitnah and the relevant Sharee‘ah regulations are observed. This is because the ruling on staying in seclusion with a non-Mahram woman (i.e. a marriageable woman) does not apply in the presence of another trustworthy woman or a group of trustworthy women, as stated by the jurists. An-Nawawi said in Sharh Saheeh Muslim: "It is impermissible for a group of men to stay alone with a non-Mahram woman, unlike the case when a man is alone with a group of non-Mahram women, as the correct opinion in this regard is that it is permissible.” [End of quote]

Allah Knows best.