What do you advise me to do regarding my wife who does not respond to my repeated advice about her immodest dress, and we have three daughters?

The hijab (definition) is an obligation for Muslim women. Firstly, one should supplicate for the guidance of the woman who does not wear the hijab. Secondly, one should continue to advise her with gentleness and kindness. This advice may come from someone other than her husband. Thirdly, if she does not benefit from the advice, repent, and wear the legal hijab, then separating from such a woman is recommended if she has neglected her obligatory duties towards Allah. However, if circumstances necessitate keeping her, there is no harm, provided that the advising continues. It is incumbent upon anyone who wishes to marry to choose a wife of good religion and character.