Does a house, in the establishment and construction of parts of which the eldest son participated, and for which there are contracts proving his ownership of some of its parts, enter entirely into the inheritance or not?

If the deceased left no heirs other than his three sons and three daughters, the inheritance is divided among them ta'siban (by agnation), with the male receiving the share of two females. That is, the inheritance is divided into nine shares (each son receives two shares, and each daughter receives one share).

Regarding the construction, if the heirs do not acknowledge that you built it, you must present lawful evidence; otherwise, you have no additional right, and everything the father left behind will be divided among the heirs according to Islamic law.

However, if the heirs acknowledge it, or if you present evidence, then the upper floor that you built, and for which there is a contract of ownership for you through your father (a gift of the house's "air rights"), will be yours.

As for the ground floor: if you completed its construction before your father's death as assistance to him, then you only have your lawful right to it through inheritance. If you completed it with the intention of partnership, then you own a share in it proportionate to what you paid. In case of dispute, the matter must be referred to the Sharia court to hear all parties.