同母 is read as どうぼ (doubo) and means same mother.
どうぼ
doubo
どうぶんぼ
common denominator
どうふぼ
the same parents
どうぼし
sisters of the same mother
おなじ
anyway
どうじ
simultaneous
どういつ
fair
どうい
same meaning
どうじん
same person
どうめい
homonym
どう
likewise
どうじょう
same as above
どうじつ
the same day