Q1: How do we reconcile Learning Mishnah at a Shiv'ah with the Halachah that an Aveil is Assur in Talmud Torah?
Q2: How may we teach Hilchot Aveilut at a Shiv'ah w/o sacrificing the Minhag of Learning Mishnayot?
A: My resolution is simple:
Learn Mishnah Elu M'galchin [M"K 3] with the Peirush haRambam. The Rambam summarizes Hilchos Aveilut in his commentary w/o much Lamdut, mainly just Halachah P'sukah.
1. There is no issur attached to the Aveil learning these inyonim
2. For the unlearned, this amounts to a pithy introduction to Hilchos Aveilut, Aveilut 101 so to speak,
Shalom and Best Regards,