My question involves insurance law for the state of: California

Four siblings had a 20-year term life insurance policy for my father. One member ("Primary beneficiary") was responsible for making payments to the term policy while the other three would pay the "primary beneficiary" on a monthly basis. There is no other beneficiaries nor % splits. They are under the agreement that they'll pay one person and that person will pay the account and it will be split evenly at the end.
They transitioned the 20-year term policy over to a whole life insurance policy after 10 years. At this time, their father was healthy and they didn't believe he would go any time soon. The transition from term to whole life would also not require another medical exam, so they all agreed to transition over to a whole life policy.
5 years later (Year 15), their father passed away.
The whole life policy was paid out and split evenly among the four siblings.
What was discovered later and unknown to anyone was that the 20-year term policy had not been cancelled. There was only a verbal and no signature made to cancel the account, so it remained active. The primary beneficiary had unknowingly been soley paying it for the remaining 5-years.

Questions:
1) Is the primary beneficiary the sole beneficiary of the 20-year term policy?
2) Are the other three siblings whom initially paid for the first 10 years of the 20-year term prior to transitioning over to the whole life policy owed any money given the fact they stopped paying 5-years ago?
3) Do the other 3 siblings have any right to the 20-year term policy benefits?
4) (Theoretical) If there was a 25% split between the 4 siblings, would the other 3 have a right to the benefits when they didn't pay for the last 5 years?