My understanding is 俩 means 两 + the measure word
for example, 俩人 means 两个人 (two people), 俩苹果 means 两个苹果 (two apples)
however, 两 is just the numeric word and doesn’t include the measure word.
@Jeremypu2019 is right. In addition to the meanings, the pronunciations are different, too.
两 [liǎng] means two which is always followed by a measure word.
俩 [liǎ] means 两个
thank you so much for your help.