  We aim to revisit the system AB Pic which has a known companion at the
exoplanet/ brown-dwarf boundary. We based this study on a rich set of
observations to investigate the companion's orbit and atmosphere. We composed a
spectrum of AB Pic b merging archival VLT/SINFONI K-band data, with published
spectra at J and H-band (SINFONI) and Lp-band (Magellan-AO), and photometric
measurements (HST and Spitzer). We modeled the spectrum with ForMoSA, based on
two atmospheric models: ExoREM and BT-SETTL13. We determined the orbital
properties of b fitting the astrometric measurements from NaCo (2003 and 2004)
and SPHERE (2015). The orbital solutions favor a semi-major axis of $\sim$190au
viewed edge-on. With Exo-REM, we derive a T$_{eff}$ of 1700$\pm$50K and surface
gravity of 4.5$\pm$0.3dex, consistent with previous works, and we report for
the first time a C/O ratio of 0.58$\pm$0.08 ($\sim$solar). The posteriors are
sensitive to the wavelength interval and the family of models used. Given the
2.1hr rotation period and our vsin(i) of $\sim$73km/s, we estimate for the
first time the true obliquity to be $\sim$45 or $\sim$135deg, indicating a
significant misalignment between the planet's spin and orbit orientations.
Finally, a proper motion anomaly between the Hipparcos and Gaia eDR3 compared
to our SPHERE detection limits and adapted radial velocity limits indicate the
existence of a $\sim$6M$_{Jup}$ inner planet orbiting from 2 to 10au
(40-200mas). The possible existence of an inner companion and the likely
miss-alignment of the spin axis orientation strongly favor a formation path by
gravitational instability or core accretion within a disk closer inside
followed by dynamical interactions. Confirmation and characterization of planet
c and access to a broader wavelength coverage for planet b will be essential to
probe the uncertainties associated with the parameters.
