What would be the "best way" to extract all people belonging to all relation path between two person

[ztlxltl]

You could try using the “Relationship path between <persons>” filter. This will return all the people needed to connect the two <persons>.

As an idea for visualizing the result, you could use my FamilyTreeView addon (still in development). Here is an example from another forum topic:

@ztlxltl

An example using the “Relationship path between <persons>” filter:

(The option “Gray out people who do not match the sidebar filter” is also used in this screenshot.)

Would something like this meet your needs?