The scene changes to Mattathias and his friends, so translators should begin a new paragraph here.

When Mattathias and his friends learned of it: Learned of it may be rendered “heard what had happened” (Contemporary English Version).

They mourned for them deeply: Good News Bible has “they were greatly saddened,” but this rendering is too weak. New American Bible is better with “they mourned deeply for them,” and so is New Jerusalem Bible with “they mourned them bitterly.” New English Bible has “Great was the grief.” Goldstein is a bit fuller with “they were deeply grieved over the victims’ fate.” Any of these renderings are possible models.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.