The midfield pair will be with the League Two side until 23 December.
Udumaga, who can also play as a striker as well as an attacking midfielder, made his senior debut in the League Cup defeat to Oxford in August and has also made three substitute appearances in the Championship.
The 20-year-old is contracted to the Bees until the end of the season.
Ferry, 18, signed a new deal earlier this week keeping him at Brentford until 2017.
He has captained the Bees’ Under-21 side for most of the season but is yet to make his first-team debut.