Maybe Jim is the protagonist who goes through various adventures and experiences. Or, he could be a key figure influencing the events in the story. Without more details, it's hard to say exactly.
You can't swim in Vice City Stories. This is a feature that wasn't included. It might have been due to technical or creative decisions during the game's development.
Yes, you can swim in GTA Liberty City Stories. Swimming can be a useful way to escape pursuers or reach areas that are otherwise difficult to access by land. However, your character's swimming ability is not unlimited, and you need to be careful not to drown if you're in the water for too long or if you're in rough waters.
In GTA Vice City Stories, swimming is not an option. The developers didn't incorporate that feature into the game. Maybe it was to keep the gameplay focused on other aspects.
Since I don't know the exact content of 'jim the farm boy part 3', I can only guess. Maybe it continues the adventures of Jim on the farm. He could be dealing with a new crop season, perhaps facing some difficulties with pests or bad weather. Or it might be about his relationship with a new character on the farm, like a neighboring farmer or a new farmhand.
The 'chance loves swim story' might be about how swimming became a form of therapy for Chance. Maybe he was dealing with stress or some kind of personal issue, and the repetitive motion and the peacefulness of the water while swimming helped him heal and find joy. He could have started swimming alone at first and then gradually joined a community of swimmers.