Oblique sitting corresponds to children who are 7.5 months of age, when the shoulder girdle is strong enough to support this position. Low oblique sitting is when the ipsilateral elbow is on the floor. In this clip my palm is touching the floor with an extended elbow, which is known as high oblique sitting.
This will improve hip external rotation mobility on the contralateral limb while simultaneously addressing ipsilateral hip abduction, scapular stability, and core strength. An additional load can be added via a kettlebell as shown here. This will increase demand of the ipsidlateral hip, core, and shoulder to elevate.
Begin this exercise with minimal load while keeping your ipsilateral knee in contact with the floor.
One progression is to elevate your knee off the floor.
You can progress this further by lifting the contralateral limb off the ground and essentially performing a weighted side plank. This will increase the demand on the hip abductors and core musculature.
Note: Make sure to keep the shoulder girdle engaged the entire time by making sure the scapula is pushed out/protracted when elevating.