Mock ESPRESSO-like time series in the sodium D2 line, for HD 209458b (R_p = 1.36 R_J; P = 3.5 d) and a mock companion (R_p = 2 R_J; P = 7 d) transiting simultaneously HD 209458 (1.16 R_⊙) with v sin i_* = 15 km s⁻¹. The transit configuration is illustrated in Fig. 2. Orbital phases are relative to the outer planet. Dotted and dashed lines show the contacts of the inner and outer planets, respectively. Top left: in-transit disk-integrated profile distorted by the occultation of the two planets. Bottom left: double-transit light curve. We note that photometric light curves are typically not an observable from ground-based spectroscopic datasets. Top right: RV derived from a Gaussian fit to the disk-integrated profile series (similar to the output of most spectrographs DRS), blending the well-known RM anomalies from the larger planet on a highly misaligned orbit (~flat deviation) and from the smaller planet on its aligned orbit (S-shaped deviation). The solid blue line show the mock Keplerian stellar reflex motion. Bottom right: 2D map of intrinsic profiles (see Sect. 6.5), showing the tracks of local stellar lines occulted by the planets along their respective transit cores.