Thanks for keeping us informed,
shaggydog.
Actually,
Groin,
Nerindel invented them as Gondorian men at arms from Æðel's noble house. So they are not technically under the rulership of Eodwine, but of Æðel; who is in Eodwine's protection.
Balvir is a captain type and Matrim is an experienced veteran of slightly lower rank. Matrim has a budding friendship with Javan. Balvir has not really been written much about.