  We are in a golden era observing Young Stellar Objects (YSOs), protoplanetary
disks, and substellar objects, crucial for understanding their formation and
evolution. This Ph.D. thesis explores two binary systems.
  Firstly, we study an eruptive YSO, HBC 494, using ALMA band 6 (1.3 mm)
observations. It's a FUor system in Orion Molecular Cloud with a resolved
binary system: HBC 494 N (primary) and HBC 494 S (secondary) separated by 75
au. The disks show hints of aligned formation scenarios, with HBC 494 N being
brighter and larger. Molecular line observations reveal bipolar outflows and
rotating envelopes. Cavity features within the continuum disks' area suggest
continuum over-subtraction or slow-moving jets and chemical destruction along
the line-of-sight.
  Secondly, we examine the young binary system $\eta$ Tel using VLT/SPHERE H
band imaging. It consists of an A-type star and a brown dwarf companion $\eta$
Tel B, separated by 208 au. Astrometric measurements over 19 years yield a low
eccentric orbit with an inclination of 81.9 degrees. The mass of $\eta$ Tel B
is determined to be 48 M$_{Jup}$, consistent with previous literature. No
significant residual indicative of a satellite or disk surrounding the
companion is detected, with limits ruling out massive objects around $\eta$ Tel
B at separations down to 33 au with masses as low as 1.6M$_{Jup}$.
  These studies employ sub-mm to near-IR observations, highlighting the
complexity of (sub)stellar formation/evolution. This thesis contributes diverse
analyses, providing insights into these intriguing processes.
