Try These Core exercises for your obliques instead of russian twists
Side Plank Variations
Side plank same knee/elbow crunch.
Side plank with hip abductions.
Form - draw your belly button in towards your spine and push your body away from the ground, especially in the shoulder; Maintain head, shoulders, hips and feet in alignment.
Side V Up
Legs straight, Arm straight .
Longer lever therefore harder.
Modification: side crunch with knees bent.
Draw belly button in towards your spine throughout exercise.
If you think these are hard, check out the plank twister challenge Dr. Jason and Dr. Julia competed in: Instagram Plank Challenge