It varies according to noun class. Jembe is part of the m/ma noun class. In that one the singular nouns correspond with the langu, lako, lake etc. possessives. The plural nouns take yangu, yako, yake etc. So my ❤❤❤ - jembe langu My hoes - majembe yangu
Jembe/majembe is (ji)/ma class so it follows the ji/ma rules. That's something you just have to memorize. But, the great thing about Swahili is that you will still be understood, even if you use the wrong noun class, in most cases.