Custody of child

I have 2years 6 months old grand daughter. My son & daughter in law are living separately in same society but in different flats for last 2 years & 3 months. They are not legally separated. My daughter in law is a doctor and stay way from home from 9A.M. to 9 P.M.. due to her work. My son is a software engineer and work from home. My wife and me are retired and stay with my son and are available full time. From 9 A.M. to 9 P.m. my grand daughter use to stay with us and we use to take full care of her besides giving her small teachings. Recently we have admitted her in a nursery school. Recently her mother has started taking child to her sisters place from 9 A.M. to 9 P.M. who is living 7 KMS away from our place only to harass us and prevent our meeting with child. Due to this child is also not able to go her school . Her sister is also software engineer and not able to devote any time on the child. Child is fully dependent on minor maid. Her father (our son) wants to take custody of child during 9 A.M. to 9P.M. as her mother is not able to contribute any thing in her upbringing and education due to her engagements. Pl suggest the remedy.