Evolution of the quadruple-star progenitor. Each row is the same as Figure 1 except this models the Be star progenitor binary (binary B). The upper panels treat the B+B binary as a single point mass with M_A = 25 M_⊙. The lower panels model a quadruple-star system. The initial eccentricity of the Be star progenitor binary is e_B  =  0.02, ω_B = 90^∘, and a_B = 0.6 au initially. The initial inclination of the B+B binary is i_A = 20^∘, and the eccentricity is e_A  =  0.02. In the left panels, the initial inclination of the Be star progenitor binary is i_B = 70^∘. The green shaded regions in the lower right panels show the approximate range where the minimum periastron separation of the Be star progenitor binary becomes small enough for the system to be a merger candidate, r_p,B < 3(R_Ba + R_Bb) = 0.14 au.