The 25 member committee known as the "golaha sare" or SRC, were members of the Army, Police and Airforce that were selectively picked in a secret meeting between Siyaad, Salaad, Caynaanshe, Samatar and few others, after a bit of double dealing and eliminating personal rivals.
For example, Xuseen Kulmiye was an Aide de Camp to PM Cigaal and was most certainly not involved in the coup, Salaad Gabeyre wanted Caydiid in his place instead. Siyaad and the others voted against that and Xuseen Kulmiye was picked - they knew that 2 Waceysles in the SRC would create intra-Abgaal rivalry, playing on Salaads power-hungry insecurities.
Siyaad eventually got his way with most of the 25 men being either his clansmen or personal friends, he knew they would vouch for him in many important votes in the future.
Those 25 men were not necessarily the coup initiators. Infact some civilians like Xasan Abshir had a bigger role in the coup than some of them.