Crystal structure, local ferroelectric and magnetic properties of the Bi1−xNdxFe1−xMnxO3 (0.05 ≤ x ≤ 0.25) ferromanganites have been studied at room temperature to reveal effect of the simultaneous Ln/Mn substitution on the multiferroic behavior of the BiFeO3 perovskite. The substitution tends to suppress polar displacements in initial rhombohedral phase to give rise to an intermediate PbZrO3-like antiferroelectric ionic arrangement at x = 0.11. Further increase of the Nd/Mn concentration stabilizes nonpolar structure specific to NdMnO3. Magnetic state of the Bi1−xNdxFe1−xMnxO3 compounds has been found to be structurally driven. The ferroelectric compounds demonstrate a dominant antiferromagnetic behavior. Magnetic field is able to modify the antiferromagnetic ordering to stabilize a weak ferromagnetic state. A threshold field inducing the metamagnetic transformation decreases with increasing the substituent's content. However, a critical Nd/Mn concentration that would yield weak ferromagnetism at H = 0 exceeds the upper limit of the compositional range of the ferroelectric phase existence, so the purely weak ferromagnetic state is realized in nonpolar solid solutions only.