Is a sister's marriage contract considered valid if her guardian was her maternal grandfather, despite the presence of the father and his initial refusal of the grandfather's guardianship, followed by his approval after the contract, and what are the implications of this after the father's death?

The aforementioned marriage is invalid due to the absence of the guardian's permission. It is obligatory to annul it and renew the contract in a proper manner. The guardian's approval after the contract has no bearing, nor does the duration of the marriage, unless a شرعي judge rules it valid, or it was performed in emulation of Imam Abu Hanifa, who does not stipulate the guardian's presence. When renewing the contract, the guardianship belongs to whoever has priority over the woman after her father. The previous marriage is considered a marriage of شبهة (doubtful validity), and the children born from it are attributed to their father, because an invalid marriage, after consummation, entails the effects of a valid marriage.