Is it permissible for a father to grant ownership of commercial shops to his minor daughters during his lifetime, while he continues to manage them, and are his brothers entitled to question the validity of this transfer of ownership after his death?

The basic principle is that an uncle has the right to dispose of his property by gifting it to whomever he wishes. For the gift to be valid, the recipient must take possession of it. If the daughters took possession of the gift during their father's lifetime, or if the money remained with him as their agent, then the gift is effective. However, if the daughters did not take possession of the gift and the father continued to dispose of the property for his own benefit, then the gift is not effective, and the shops are considered an inheritance to be divided among all heirs.