他俩 already contains 'two', so never say 他两个. Same shape with other pronouns: 我俩 (the two of us), 你俩 (you two).
mistakes
Don't confuse 俩 (liǎ, 'two of') with 两 (liǎng, 'two'). 俩 acts as a pronoun-suffix that already includes the measure word; it cannot be followed by another measure word.
