Relation of two child custom objects under the same parent object

Summary

is this possible to derive a field value in Child A from Child B of the same parent

Content

I need help that we have one parent object Account and under this we have two custom child objects Child A and Child B. Child A has one filed named: Points and i want this field to be derived from another field in child object B. is this possible using groovy?

 

BR,

Yasir