no that's wrong. "Küçük yengeç onlarda" means that the crab is with them, for example at their apartment. Just like the English version "I have the X". You wouldn't say "I have the X" to imply that you possess an X. You would only use it in such a case
- Where are the X and Y that I saw yesterday?
- I have the X, Adam has the Y.
When you mean you possess something, you don't use "the".
I have a car - Benim (bir) arabam var.
I have cars - Benim arabalarım var