What is the ruling of the Sharia on uncles sponsoring their brother's daughters after their mother seized their money and they refused to live with her due to her bad character, and are they considered their guarantors?

The default rule for child custody after a couple's separation is that it belongs to the mother, unless there is a impediment to custody. Among these impediments is if the custodian resides in the same country as the ward's guardian. When the children reach the age of discretion, they are given the choice to live with whichever parent they wish, provided that both parties are eligible custodians. If the mother is immoral or untrustworthy with the children, or if she travels to another country, her right to custody is forfeited. If the mother infringes upon the rights of the heirs, the matter should be brought before the court to rectify this injustice. However, this does not nullify the mother's rights over her children, and it remains obligatory for them to treat her with kindness and excellence.