Self-identification begins at birth and has less to do with the objective facts than it does with our interpretation of events and interactions of others with us and each other -- it is a web spun of perceptions and interpretations. This is not a matter of objective relationships, which have also been seriously altered, but of their perceptions and interpretations of those relationships, and THOSE are seriously ruptured.
I will always be, have always been, myself, but my place among others, my status, my rank, my social network -- just about all else has been "taken apart" more than once. And yes other people OBJECTIVELY remained the same, but not my perception of them, nor their perception of me. And that causes different responses, mine and theirs.
Destruction of our web "changes things". Everything has changed for those two men. They had a father stripped away. And because their "father" wasn't their father, their objective relationship to him and to their "cousin" Gaile is broken, it does not exist. It sound very much as if they are not biologically related to Gaile. So who are they, the web they had is torn apart, and where is the one that each one might fit into? If all they have in common biologically is the same mother, they have to find their place in her web of relationships.
Break one strand, you can end up breaking a lot of the others.