  We report new photometric and spectroscopic observations of the K2-99
planetary system. Asteroseismic analysis of the short-cadence light curve from
K2's Campaign 17 allows us to refine the stellar properties. We find K2-99 to
be significantly smaller than previously thought, with $R_{\star} =
2.55\pm0.02$ $\mathrm{R_\odot}$. The new light curve also contains four
transits of K2-99b, which we use to improve our knowledge of the planetary
properties. We find the planet to be a non-inflated warm Jupiter, with
$R_\mathrm{b} = 1.06 \pm 0.01$ $\mathrm{R_{Jup}}$. Sixty new radial velocity
measurements from HARPS, HARPS-N, and HIRES enable the determination of the
orbital parameters of K2-99c, which were previously poorly constrained. We find
that this outer planet has a minimum mass $M_\mathrm{c} \sin i_\mathrm{c} =
8.4\pm0.2$ $\mathrm{M_{Jup}}$, and an eccentric orbit ($e_\mathrm{c} = 0.210
\pm 0.009$) with a period of $522.2\pm1.4$ d. Upcoming TESS observations in
2022 have a good chance of detecting the transit of this planet, if the mutual
inclination between the two planetary orbits is small.
