Hindi:
Maternal grandmum: Nani
Maternal grandad: Nana
Paternal grandmum: Dadi
Paternal grandad: Dada

Tamil:
No genealogical distinction
Grandmums: Pati
Grandads: Thatha

Malyalam:
Mum: amma; dad: acchan (cch, as in, change)
Maternal grandmum: ammamma
Maternal grandad: ammachhan
Paternal grandmum: ?? (Ravi, help!)
Paternal grandad: Acchacchan