Zaid, Bakr, Amr and Khalid are four partners in a Shirkat venture.

Answer

The fact that Amr is no longer regarded capable of decision-making by the other partners confirms his mental incapacity. Since he has effectively no say in the affairs of the business due to his mental state, the partnership in respect to him has terminated.

The first step which is Waajib on the remaining partners is to assess the financial state of the business and to calculate Amr's share.

The second Waajib step is to hand over Amr's share to whoever will be his Trustee to oversee his (Amr's) affairs.

His adult son being his wali, will be the trustee. The son will be his mentally incapacitated father's curator. His curatorship in terms of the secular law of the land is further enhanced and confirmed by the General Power of Attorney which his father had given him and his two sisters.

Consensus of the heirs is not a necessary Shar'i requisite for the son to be appointed the curator. The son is in charge of his mentally incapacitated father and even of his body after his (the father's) death. The son has a prior right over his uncles (father's brothers).

Since Amr is no longer a partner in the Shirkat company due to the termination of the partnership in respect to him, the question of making decisions on his behalf regarding the Shirkat affairs is superfluous. The curator (the son in this case) only has the right to demand from the remaining partners payment of his father's share.

The son may, however, enter into a fresh partnership contract with the other partners on behalf of his father if they are agreeable.

The remaining partners are no longer the wakeels of Amr due to the termination of the partnership. The wikaalat remains valid only as long as the Shirkat is valid. The wikaalat lapses with the termination of the Shirkat.