Two components of the boundary of \(\text \textbf{I}_3\). (Deux composantes du bord de \(\text \textbf{I}_3\)) Families of Calabi-Yau elliptic fibrations in \(\mathbb{P} (\mathcal{L}^a\oplus\mathcal{L}^b\oplus\mathcal{O}_B)\) 