Meanwhile, Leonello's younger legitimate brothers were also vying for the same position. Because of the potential political conflict that could arise between these siblings, Leonello's father was very cautious of officially appointing Leonello as his successor. Although Leonello was able to co-rule with his father since 1434, Niccoló waited until his last will, which was written just before his death, to formally recognize Leonello as his heir. Niccoló's final will also protected the claims of his legitimate sons Ercole and Sigismondo and ensured that they were each given 10, 000 ducats. Following his father's death in 1441, Leonello finally became recognized as the formal heir and the new Marquis of Ferrara.