The father said: I give my daughter in marriage to So and so, in front of Muslim witnesses, then he changed his mind and recanted his words

A father says that he giveshis daughter in marriage to X in front of
Muslim witnesses, including two males, and gives them permission to
inform friends and family relatives about it. After everybody has been
informed and the boy has given the mehr to the girl,the father changes
his mind.
Is it permissible for the father to stop them from starting to live
together? Are they considered to be married or not?
Praise be to Allah.
The marriage contract is completed with the proposal and acceptance.
The proposal is when the wife's guardian says, "I give So and so to
you in marriage." The acceptanceis when the groom says, "I accept" or
"I accept marriage to So and so." It is not essential for it to bein
these exact words; rather the marriage contract is completed by
whatever phrases indicatemarriage.
Shaykh Ibn 'Uthaymeen (may Allah have mercy onhim) said: The basic
principle is that all contracts are completed by means of whatever
signifies them according to custom, whether it is inthe words
mentioned or otherwise, in the case of the marriage contract andother
contracts. This is thecorrect opinion and it is the view favoured by
Shaykh al-Islam Ibn Taymiyah (may Allah havemercy on him).
End quote from ash-Sharhal-Mumti', 12/40
And he (may Allah have mercy on him) said: Some of the scholars
stipulated specific phrases in some contracts and said that they must
be used, as in the marriage contract for example, where they said that
it is essential (for the guardian) to say: "I give to you in
marriage…", andfor (the groom) to say, "I accept."
Other scholars say that all contracts are completed by means of
whatever phrases signify them according to custom. This view is the
one that is correct, and this is the view favoured by Shaykh al-Islam
Ibn Taymiyah (may Allah have mercy onhim), because transactionsare not
acts of worship in which one should adhere strictly to what has been
narrated; rather they are transactions between people. So whatever
people regard as a sale is a sale, whatever they regard as a pledge
(or mortgage) is a pledge (or mortgage), whatever theyregard as a waqf
(endowment) is a waqf, and whatever they regardas marriage is
marriage.
The correct opinion is thatthere is no specific format for any
contract; rather the contract is completed by means of that which
signifies it, and no one can prove that there is any difference
between sale transactions and other types of transactions. If they
say, for example, that Allah mentioned marriage by using the word
nikaah, we say: likewise, He mentioned sales by using the word bay';
are you saying that it is essential to say, "Bi'tu (I have sold)"?
They will say that this is not essential, as buying and selling are
done by whatever wording signifies that according to custom, witha
proposal and acceptance(after the proposal).
End quote from ash-Sharhal-Mumti', 8/101
If the father of the girl said: "I have given my daughter in marriage
to So and so," and the husband responded in a way that signified
acceptance, then the proposal and acceptance have taken place.
Moreover, there are essential conditions for marriage which must be
met: there should be consent from both spouses, and the
marriagecontract should be done by the woman's guardian issuing his
proposal in thepresence of two witnesses. If these conditions were
met, thenthe marriage has been done and the guardian does not have the
right toretract it or annul it unlessthere is a reason that makes
annulment permissible, such as annulment due to a physical defect (in
one of the spouses) or annulment for going against the conditions.
Our advice is to refer the matter to a scholar whomyou trust, so that
he can listen to the guardian, andthe husband and wife.
We ask Allah to help and guide us and you.
And Allah knows best.