Our late father's will gives all his property to one child. Must we follow it?

No; a will to an heir does not take effect without the other heirs' consent, and a will cannot exceed one third of the estate. This means such a will cannot be carried out as written. The property is still divided by faraid, unless all the adult heirs willingly agree to honour their late father's wish. You are not sinning by not following a will that conflicts with Islamic law. But guard your tongue about your late father and about the sibling named in the will; he may never have asked for it himself. Take the original will to the estate officer or the Syariah Court to be assessed. See wills to heirs.