lenght variables

[Willy Henkens]

Suppose a column :

12345 (grandfather)
123450 (grandmother)
123451 (grandfather's first child)
1234511 (grandfather's first grandchild from first child)
1234512 (grandfather's second grandchild from first child)
1234513 (grandfather's third grandchild from first child)
123452 (grandfather's second child)
1234521 (grandfather's first grandchild from second child)
1234522 (grandfather's second grandchild from second child)
and so on...
...
123456 (grandfather's sixth child)
1234561 (grandfather's first grandchild from sixth child)
and so on...
On their turn, every child or grandchild can be grandfather or grandmother in the future.

These numbers are selected as text (and not as number!), to enable sorting them in the way as they appear as such.

Question : when I have one value which is unique for 1 person in the ancestry, e.g. 125663 :
1) How can I select the record of the father, (having the number 12566), and the mother, (having the number 125660) ?
2) And further: how can Y select all the children 125661 , 125662, 125663 etc...having all 1 additional digit only and NOT the grandchildren having more digits?
In the event, on a given number, one need to search the number with one digit less and all the numbers having only one digit more.
Can somebody help me, please? Or advise me how to proceed ?