Is an engagement considered binding merely upon the preliminary approval of the families, or is it stipulated that there be an announcement and public declaration for the interaction between the two parties as fiancés to be valid?

What happened between the young man and the girl's family is called 'murakanah' (mutual inclination/agreement), which is the manifestation of consent, or a negotiation from which each party understands the other's submission to their condition and their desire for the contract, even if a dowry has not been stipulated. It is not a condition to publicize it among people. This 'rukun' (inclination) does not permit anything that was forbidden between the suitor and the one being sought. Rather, its fruit is the prohibition of proposing to this woman who has been 'murakanah'. The young man and the young woman are still strangers to each other until the marriage contract is concluded. The proposal only permits looking at the one being sought to the extent that it encourages her marriage.