  For a pair of supermassive black holes (SMBHs) in the remnant of a dual
galaxy merger, well-known models exist to describe their dynamical evolution
until the final coalescence accompanied by the emission of a low-frequency
gravitational wave (GW) signal. In this article, we investigate the dynamical
evolution of three SMBH triple systems recovered from the ROMULUS25
cosmological simulation to explore common dynamical evolution patterns and
assess typical coalescence times. For this purpose, we construct initial
conditions from the ROMULUS25 data and perform high-resolution gravitodynamical
\N-body simulations. We track the orbital evolution from the galactic inspiral
to the formation of hard binaries at sub-parsec separation and use the observed
hardening rates to project the time of coalescence. In all cases, the two
heaviest black holes form an efficiently hardening binary that merges within
fractions of the Hubble time. The lightest SMBH either gets ejected, forms a
stable hierarchical triple system with the heavier binary, forms a hardening
binary with the previously merged binary's remnant, or remains on a wide
galactic orbit. The coalescence times of the lighter black holes are thus
significantly longer than for the heavier binary, as they experience lower
dynamical friction and stellar hardening rates. We observe the formation of
hierarchical triples when the density profile of the galactic nucleus is
sufficiently steep.
