can a father/husband force his child/wife to accept the view which he thinks is correct in case of ijtihadi masalah where there is ikhtilaaf among the ulama? i.e. covering the face, doing raful yadayn, reciting fatiha behind imam....

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Some scholars reported the difference of opinion concerning the ruling on obeying someone whom one is in principle obliged to obey, like the father or the husband, if they ordered him to do what he believes to be forbidden, or they prohibited him from doing what he [i.e. the person who is ordered] considers to be obligatory; and these are issues of difference of opinion and Ijtihaad.

Al-Iz ibn Abus-Salaam said in Qawaa'id al-Ahkaam:

“Rule about whomever one is obliged to obey, and one whom a person is not permitted to obey: there is no obedience to any of the creatures, except for those whom Allah has authorized to obey, such as the Messengers, the scholars, the Imams, the judges, the governors, the fathers, the mothers, the masters [i.e. those who own slaves] and the husbands. If the Imam or ruler orders a person to do what they [the one who gives the order] believe to be permissible while the person who is ordered believes that it is forbidden, then does he have to do it according to the view of the one who orders him, or is he permitted to abstain according to his view [i.e. the one of the one who is ordered]? There is a difference of opinion (on this issue).” [End of quote]

The most preponderant opinion is that obedience is not permissible in doing what is forbidden and abandoning what is Wajib (obligatory) according to the view of the one who gives the order; this is contrary to what is outside the circle of obligation and prohibition. The most preponderant opinion is that obedience is obligatory in the limits of the ability of the one who is ordered and what does not lead to any harm.

With regard to the examples that are mentioned in the question, if the woman is of the view that it is an obligation to cover the face, while the husband is of the view that it is only recommended, or when the person ordered is of the view that it is an obligation to recite al-Faatihah in prayer while the person who gives the order is of the view that it is not an obligation, then he [i.e. the person who is ordered] is not obliged to abide by the view of the person who orders him to do so, and he is not permitted to obey him in that.

With regard to the question of raising the hands in prayer, then if the person who gives the order is of the view that it is legislated to do so, and the one who is ordered is of the view that it is not recommended (desirable) to do so, then the most preponderant opinion is that it is obligatory to obey him according to his ability.

Allah knows best.