The most prominent of the miscellaneous Section XIII members is, of course, Father Renaldo.
In the manga his sole purpose is to show up and deliver some information to Alex. In the TV anime his sole purpose is to stand behind Enrico and hold up a FREAK
In the museum scene, when Alucard enters, Enrico discreetly steps behind Father Renaldo, who takes a "ready-to-fight" stance. Apparently he has some value as a bodyguard. We never get to see it, though.
He's probably secretly an international drug czar, or something.
In addition to Father Renaldo, though, there's a whole legion of Iscariot soldiers. They're not assassins like Heinkel and Yumie; they're a mass force, deployed as an army.
Finally, there's a full complement of paper-pushers and informational assistants, including one nervous and cute young messenger boy.
Why obsess over Father Renaldo? Because he's totally gangsta. What about the rest of Iscariot? Well, they're all cannon fodder anyway, so there's no reason to spend much energy worrying about them. Except the Nervous Messenger Boy. He's too cute to die.