I would like to ask if there is a specific way of positioning of legs while sitting in Tashahud or in between the sujood in namaaz?

Is it wajib to position legs in a particular way?

What if one does otherwise? eg. keeping left ankle on top of right or just sitting on both the legs?

Ruling 1089. It is recommended that while saying tashahhud, one should sit with his weight placed on his left thigh, and place the front of his right foot on the sole of his left

This is recommended. If not (possible) you sit as is possible for you