In Shariah law, there is a clear distinction between gifts given to offspring during the parent's lifetime (hiba) and inheritance, which is distributed after death. The shares of inheritance are predetermined by Sharia and cannot be altered. Therefore, if, during his lifetime, a father gives some part of his assets to an offspring and also transfers possession of it, this does not mean that the offspring will then not be entitled to a share in the remaining assets when the father passes away.
In the situation described in the question, the shares given to the sons by the father during his lifetime will be considered as a "hiba" if the father also transferred possession of the shares. As a result of this "hiba", these sons will still be entitled to a share in the remaining assets when the father passes away. In other words, receiving the "hiba" will not exclude them from inheriting the remaining assets alongside the other rightful heirs.
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دلائل:
تکملۃ رد المحتار: (کتاب الدعوی، 505/6، ط: سعید)
الارث جبری لایسقط بالاسقاط.
البحر الرائق: (کتاب الفرائض، 346/9، ط: رشیدیہ)
وأما بيان الوقت الذي يجري فيه الإرث فنقول: هذا فصل اختلف المشايخ فيه، قال مشايخ العراق: الإرث يثبت في آخر جزء من أجزاء حياة المورث، وقال مشايخ بلخ: الإرث يثبت بعد موت المورث".
Allah the Almighty knows best.
Darul ifta Al-Ikhlas, Karachi.