  Weakly bound and unbound three-body nuclei are studied by using the
pseudostate method within the hyperspherical formalism. After introducing the
theoretical framework, the method is applied first to the $\boldsymbol{^9}$Be
nucleus, showing a good agreement with the available data for its low-lying
dipole response. Then, recent results on the structure and decay of the
two-neutron emitters $\boldsymbol{^{26}}$O and $\boldsymbol{^{16}}$Be are
presented. In particular, the role of the $\boldsymbol{n}$-$\boldsymbol{n}$
correlation in shaping their properties is discussed.
