What is the ruling on marrying two maternal stepsisters at the same time?
Is this permissible or is it considered Haram (prohibited) due to the generality of the prohibition of marrying two sisters at the same time?
There is no doubt that maternal stepsisters are still considered sisters. The prohibition of marrying two sisters at the same time is general, whether they were full or foster sisters, free women or slaves, or a free woman and a slave, whether paternal or maternal half sisters, and whether before or after consummating the marriage. This is according to Allah's Saying:
...and two sisters in wedlock at the same time, except for what has already passed
Ibn Al-Mundhir said that the scholars unanimously agreed to it. (Part No. 18; Page No. 231) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.