While discussing verse 4:15
Those who commit unlawful sexual intercourse of your women - bring against them four [witnesses] from among you. And if they testify, confine the guilty women to houses until death takes them or Allah ordains for them [another] way.
Imam al-Qurtobi commented in his tafsir saying :
ولا بد أن يكون الشهود ذكورا ؛ لقوله : ...
Provided you are not alone with them then it is permitted for you to sit with your sisters in law if they are wearing a headscarf and dressed modestly.
But you should guard against sin and lower your gaze, especially if you are attracted to one of them. Modesty falls equally on men and women and you must observe hijab.
If you are unable to resist ...