After another series of shogunate victories on the outskirts of Osaka, the Summer Campaign came to a head at the battle of Tennōji. Hideyori planned a hammer-and-anvil operation, in which 55,000 men would attack the center of the Eastern Army, while a second force, 16,500 men led by Kyōgoku Tadataka, Ishikawa Tadafusa, and Kyōgoku Takatomo, would flank them from the rear. Another contingent waited in reserve. Ieyasu's army was led by his son, the Shogun Tokugawa Hidetada, and numbered around 155,000. They moved in four parallel lines, prepared to make flanking maneuvers of their own. Mistakes on both sides nearly ruined the battle, as Hideyori's ronin split off from the main group, and Hidetada's reserve force moved up without orders from the main force. In the end, however, Hideyori's commander Sanada Yukimura was killed, destroying the morale of the Western Army. The smaller force led directly by Hideyori sallied forth from Osaka Castle too late, and was chased right back into the castle by the advancing enemies; there was no time to set up a proper defense of the castle, and it was soon ablaze and pummeled by artillery fire. Hideyori committed seppuku, and the final major uprising against Tokugawa rule was put to an end, leaving the shogunate unchallenged for approximately 250 years. According to an account by an employee of the Dutch East India Company in Hirado, several daimyō set the castle on fire and attempted to defect to Ieyasu. Hideyori executed them by throwing them off the castle wall but could not extinguish the fire, causing his suicide. The account also stated that about 10,000 people died. History indicates that the legendary swordsman Miyamoto Musashi participated in the battle on the Toyotomi side, though he has no recorded accomplishments in this battle.
Question: How many leaders led the second force to flank them from the rear?
Answer: 3