sir, please see that you have to do for your mother"s side. Also this will clarify your doubt.
Names of grand mother, great grand mother, Fathers great grand mother if mother is alive
[2] In case mother is alive, this would be pithamahi-prapithamahi-pithruprapithamahischa
[3] In case mother’s mother is alive , this would be mathamahasya mathu-pithamahi-prapithamahischa
[4] Mesharavi punya kale for tharpanam done on Mesha sankramam(chittirai-makaram first)Karkadaga ravi punya kale( for tharpanam done during adi=Karkidaga Sankramam(Adi first), Thula ravi punya kale for tharpanam done during thula masam first(Iyppasi first), makara ravi punya kale for tharpanam done on makara
sankramam(Thai first), Suryoparaga punya kale for tharpanam done during solar eclipse, Somoparaga punyakale for tharpanam done during Lunar eclipse and In case of Paraheni tharpanam done after Sraddham, “Purvedya maya krutha mathru pithru prathyabdhika sradhangam thila tharpanam karishye. Please note in case of paraheni tharpanam, the offering(tharpanam) is made to only paternal side pithrus.
[5] In case mother is alive, this would be pithamahi-prapithamahi-pithruprapithamahischa
[6] In case mother’s mother is alive , this would be mathamahasya mathu-pithamahi-prapithamahischa
[7] If mother is alive instead of mathru tharpanam perform pithamahi tharpanam.In the manthras replace mathu with pithamahi.
[8] If mother is alive instead of pithamahi tharpanam perform prapithamahi tharpanam.In the manthras replace pithamahi with prapithamahi
[9] If mother is alive instead of prapithamahi tharpanam perform pithru prapithamahi tharpanam.In the manthras replace prapitha mahi with pithru prapithamahi.
[10] If maternal grand mother is alive instead of matha mahi tharpanam perform matha mahasya mathu tharpanam.In the manthras replace mathamahi with mathamahasya mathu.
[11] If maternal grand mother is alive instead of mathu pithamahi tharpanam perform matha mahasya pithamahi tharpanam.In the manthras replace mathu pithamahi with matha mahasya pithamahi
[12] If maternal grand mother is alive instead of mathu prapithamahi tharpanam perform mathamahasya prapithamahi tharpanam.In the manthras replace prapitha mahi with matha mahasya prapithamahi.
[13] If mother is alive recite Pithamahi-prapithamahi-pithru prapapitha maheebhyo nama
[14] If maternal grand mother is alive then Mathamahasya mathu-mathamahasya pithamahi-matha mahasya prapithamaheebhyo nama.
[15] People doing tharpanam on one koorcham chant” Asmaath koorchat vargodvaya pithrun yathastanam prathishtapayami.”