Biological Mother's name change in child's document

Hello all, I am a male with a 8-year old son. I got divorced and now remarried. I have full custody of the child with visitation rights for biological mother of the child in my presence. The child's Aadhaar card, passport, school register and birth certificate -- everything has his biological mother's name in those. My queries: 1) Can the biological mother's name be changed to my current wife's name in these documents without the legal adoption process by her? Is legal adoption the only process? 2) If legal adoption the only process, is obtaining NOC from my ex-wife is only involvement from her end, or does she need to be present in more steps? 3) Is it possible to change "mother's name" in passport, without changing it in birth cert.? Or changing the mother's name in birth cert. is mandatory, before changing the name elsewhere? 4) I am little confused (considering the possible/feasible legal issues in future, if any) whether it is better to update my current wife's name in place of "mother" in my son's documents (school, passport), or should I just leave the docs. like that [with his bio. mother's name]? It will be great help to understand these before proceeding with any required process by me. Thank you.