About the clipping of nails and cutting of hair during dhul hijjah

Asalamualikum My dad says that he heard a maulana say that in the 10 days of dhul hijjah the ruling of cutting the nails and hair is only for the person performing hajj and in the state of ihram and not applied to the person not performing hajj but intending to sacrifice an animal. So I want to know whether this is right or not. And also I have read that it is only for the person paying for the sacrifice or slaughtering himself to not cut hair or nails but the family members on whose behalf the sacrifice is being offered are permissible to cut hair and nails. So is that true? Eg if my dad is paying for the udhhiyah on our behalf but we do intend for the sacrifice so is it permissible or not permissible for us to cut the hair or nails?