The Porcupine Warriors are continuing their pre-season preparations in the capital, and the inclusion of the pair signals their imminent arrival at the club.
Mammah, a highly rated forward previously with Samartex, has been the subject of interest from several clubs. Yakubu, a former Dreams FC centre-back, also joins the group as Kotoko strengthen their options ahead of the new campaign.
Official confirmation of the deals is anticipated shortly as the club finalises formalities for the two new additions.