Yes, MOTHERS is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, T 1, H 4, E 1, R 1, S 1.

Is it a valid word?

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

a woman who has given birth to a child (also used as a term of address to your mother)
a stringy slimy substance consisting of yeast cells and bacteria; forms during fermentation and is added to cider or wine to produce vinegar
a term of address for an elderly woman
a term of address for a mother superior
a condition that is the inspiration for an activity or situation

Also: female parent, bring forth.