Yes, DESCENDERS is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, S 1, C 3, E 1, N 1, D 2, E 1, R 1, S 1.

Is it a valid word?

DESCENDERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

someone who descends
a lowercase letter that has a part extending below other lowercase letters
(printing) the part of lowercase letters that extends below the other lowercase letters