Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
The Nyindu variety is heavily influenced by Lega, and speakers consider it a dialect of Lega rather than Shi, as Shi speakers see it. Maho (2009) leaves it unclassified as JD.501.
The people who speak Mashi are known as Bashi. They are the largest tribe in South Kivu, whose capital city is Bukavu.
The Bashi occupy a vast region known as Bushi. Like Ngweshe, Kabare, Katana, Luhuinja, Burhinyi, Kaziba, Nyengezi, and Idjui where live the Bahavu who are also part of this group; Idjui is a large island in Kivu lake between DRC and Rwanda.
References
Shi at Ethnologue (18th ed., 2015) (subscription required) Nyindu at Ethnologue (18th ed., 2015) (subscription required)