How to save one to many records

We have 3 records in our application say record A, record B and record C. Record A is having one to many relation with record B where record B is having one to many relation with record C. Record A is having generic details, record B is having section details which can be multiple and record C is having one editable grid having multiple entries which is present in the above section. We are facing issue while displaying and saving the value into the rule input since we are not able to use [fv!index] for record variables. We are using only one rule input of record type A. How to make sure to show the values properly and save them properly?? 


This is just a mock UI i created for explaining the issue. Add member will add one more row in developer details grid. Add Team will repeat the whole section again.