Is it permissible to secretly عقد قران (solemnize a marriage contract) with a minor girl, with the consent of her maternal grandfather—who has taken on her upbringing—and the refusal of her negligent father, with the intention of completing the marriage after she reaches 18 years of age, and then publicly renewing the contract?

The Shari’ah encourages marriage between two who love each other. The girl's father is her guardian (wali), and the fact that he did not undertake her upbringing does not negate his guardianship. Therefore, the marriage contract cannot be concluded without his permission. The guardian is a condition for the validity of the marriage according to the most authoritative opinion. Her maternal grandfather is not among the guardians. The questioner is advised to try to persuade her father to agree to the marriage. There is no harm in delaying the consummation until she reaches the age of eighteen, in compliance with the country's law. If he is not convinced, then he should look for someone else.