1) It can be on cruelty ground.
2) Yes mutual consent divorce will be fast instead of judicial separation.
3) You can tell court that in last 3 years you are
came together physical relationship.
4) Yes, the 6 months to 18 months and cooling period clause is the same.
5) No, they can't force you to stay together, if you have filed for divorce.
6) Mother will get child custody as child is minor.
Nobody can stop her doing all these things of legal proceedings. As she also has all legal rights to live as per constitution.