Unbound states in $^{24}$O and $^{23}$N were populated from an $^{24}$O beam at 83.4 MeV/u via inelastic excitation and proton knockout on a liquid deuterium target. Using the MoNA-LISA-Sweeper setup, the decay of each nucleus could be fully reconstructed. The two-body decay energy of $^{23}$N exhibits two prominent peaks at $E = 100 \pm 20$ keV and $E=960 \pm 30$ keV with respect to the neutron separation energy. However, due to the lack of $\gamma$-ray detection, a definitive statement on the structure of $^{23}$N could not be made. Shell model calculations with the WBP and WBT interactions lead to several interpretations of the spectrum. Both a single state at 2.9 MeV in $^{23}$N, or two states at 2.9 MeV and 2.75 MeV are consistent with the shell model and data. In addition, a two-neutron unbound excited state of $^{24}$O, populated by $(d,d^{'})$, was observed with a three-body excitation of $E = 715 \pm 110$ (stat) $\pm 45$ (sys) keV, placing it at $E = 7.65 \pm 0.2$ MeV with respect to the ground state. Three-body correlations for the decay of $^{24}$O $\rightarrow ^{22}$O + 2n show clear evidence for a sequential decay through an intermediate state in $^{23}$O. Neither a di-neutron nor phase-space model were able to describe the observed correlations. This measurement constitutes the first observation of a two-neutron sequential decay through three-body energy and angular correlations, and provides valuable insight into few-body physics at the neutron dripline.
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