Worked for 3 others so far.

.....from my "work" PC...
To be expected. Firewall.
Try at home.

Find the intersection of the 3 calculated curves,
either by inspection or calculations.
https://www.mediafire.com/file/cum1y5hij3k5kqn/02_02_22a.pdf/file

Excel 365 Pro Plus with Power Pivot and Power Query.
Three ways:
https://www.mediafire.com/file/77oe6mpz672ho9a/11_21_21.xlsx/file
https://www.mediafire.com/file/j211e1pmx6wcy30/11_21_21.pdf/file

No formulas

Don't fix what ain't broken.
Needed from you: Complete 3Mb shared file.
Needed by you: Three months of PQ/PP training.
Needed by me: Patience.

Randomly select a given set (25% in this example) of persons
from a variably sized population of last names.
With the latest formulas, Defined Names and PQ.
Updated files.
Rohn007 has posted a plethora of pointers to PQ Putorials perpetually.

Pass.
Seems you just copied and pasted my example and fiddled with it.
You need to learn PQ and its "M" programming language,
Hope to hear from you in three months.

I defer to LZ's better solution.

See Wikipedia "Linked List"
Your unknown real data may be a
Singly/Doubly/Multiply and/or Circular Linked List
with Sentinel Nodes/List Handles and/or Pointers,
each type requiring a unique program for analysis.
My solution assumes a Singly Linked List with one List Handle.
I added a calculated tree diagram and a tweaked LZ program.
Same file link.

Your data has three generations, not two.

You're so jolly right.
Updated file.
Same link.