Who is the guardian of a 21-year-old mature girl after the death of her father, given the presence of her mother and paternal uncle, and does any of them, or her elder sister's husband, have the right to object to her engagement?

The person most entitled to give a woman in marriage is her father, then her male relatives in order of closeness. If the right of the closer relative falls away, it transfers to the next in line.

If the right of all her relatives falls away, then the ruler is the one who marries her off, and the judge acts on his behalf, for the Prophet, peace and blessings be upon him, said: "The ruler is the guardian of she who has no guardian."

In the case of this girl, the guardianship transfers to her paternal uncle in the absence of a closer relative, and not to her sister's husband. This is regarding the guardianship in marriage.

As for the guardianship of wealth, it is only established for the father, the guardian (appointed), the grandfather, and the judge. It is not established for others, such as the brother or paternal uncle, except through an appointment from the father or the judge.