  The possible bound nuclei beyond the two-neutron drip line in the
$50\leqslant Z \leqslant 70$ region are investigated by using the deformed
relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the density
functional PC-PK1. Bound nuclei beyond the drip line of $_{56}$Ba, $_{58}$Ce,
$_{62}$Sm, $_{64}$Gd and $_{66}$Dy are predicted, forming peninsulas of
stability in the nuclear landscape. Near these peninsulas, there are several
multi-neutron emitters which are stable against two-neutron emission but
unstable against multi-neutron emission. The underlying mechanism is
investigated by studying the total energy, Fermi surface, quadrupole
deformation and single-neutron spectrum in the canonical basis. It is found
that the deformation effect is crucial for the peninsulas of stability, and
pairing correlations are also essential in specific cases. The dependence on
the deformation evolution for the stability against neutron emissions is
discussed. %Taking Ba and Sm isotopes near the drip line as examples, the
evolution of the canonical single-neutron spectra and pairing energies are
discussed in detail to further understand the mechanism in a microscopic way.
