This is the 5895th most frequent Turkish word.
teknelerinin
"Of their boats."
In this sentence, 'teknelerinin' is used as a possessive noun form meaning 'of their boats,' referring to the fishermen's boats.
Balıkçıların teknelerinin motorları bozulmuş.
The engines of the fishermen's boats are broken.
Here, 'teknelerinin' indicates possession, specifying 'of the boats belonging to the friends of my brother.'
Kardeşimin arkadaşlarının teknelerinin boya işleri yapılacak.
The paintwork of the boats of my brother's friends will be done.
In this instance, 'teknelerinin' denotes ownership, referring to 'of the boats of the harbor.'