Developing a thesis statement is an important step in writing a good paper, and it's best to have your thesis picked out before you begin writing. Once you have it, you can decide on your evidence, transitions and overall structure. For "Squatter," there are a few angles you can take, all equally valid as long as you support them strongly.
A good thesis for this story will be focused on the morals of the two stories Nariman tells. A smart idea would be to find common ground between the two stories and try to find one lesson that they both impart, or one lesson that is made stronger with evidence from both stories. For instance, Nariman's first story about the master cricket player is covertly about a man who tries many things and never finds happiness. At its core, this story is about knowing oneself and ones own true identity. The second story, about Sarosh the squatter, hits upon similar lessons. He emigrates to Canada only to find that he can never fully fit in and become part of their culture. In a way, he denies his own identity and realizes he can never truly escape who he is. In that way, a good thesis could be something like:
"Squatter" utilizes the two word-of-mouth stories told by Nariman to establish the fact that one must accept and celebrate their own true identity.
Of course, that's just one idea, and there are many to work with, but that could be a good starting point. Another good idea could be the importance of community, as evidenced by the boys gathering to hear Nariman's story, as well as the fact that Sarosh leaves his community and suffers for it. Good luck!