SkyWarsIsland.java

import org.bukkit.Location;

public class SkyWarsIsland
{

    private Location[] spawnLocations;

    public SkyWarsIsland(Location[] spawnLocations)
    {
        this.spawnLocations = spawnLocations;
    }

    public Location[] getSpawnLocations()
    {
        return spawnLocations;
    }
    
    // TODO: more relevant methods
}

SkyWarsTeam.java

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;

import java.util.*;


public class SkyWarsTeam
{

    private Set<UUID> players;
    private SkyWarsIsland island;

    public SkyWarsTeam(SkyWarsIsland island)
    {
        this.island = island;
        this.players = new HashSet<>();

    }

    public Collection<Player> getPlayers()
    {
        Set<Player> players = new HashSet<>();

        getPlayers0().forEach( player -> players.add( Bukkit.getPlayer( player ) ) );

        return Collections.unmodifiableSet( players );
    }

    private Set<UUID> getPlayers0()
    {
        return players;
    }
    
    public SkyWarsIsland getIsland()
    {
        return island;
    }

    public void addPlayer(Player player)
    {
        getPlayers0().add( player.getUniqueId() );
    }

    public void removePlayer(Player player)
    {
        getPlayers0().remove( player.getUniqueId() );
    }

    // TODO: impl relevent methods
}