So Garling told his twin how he would kill his mother...

I think Garling found out that the woman he fucked had children.

He wants to take the children away, but the woman was against it. Garling has a pure CD wife in Mary Geoise, who is infertile, and Garling needs a heir and spare.

Garling made Shanks's mom a prey in the hunting games.

When Rocks suddenly attacked God Valley, Shanks's mom fled to take the children and try to escape