I've been breeding my Vault Dwellers together pretty indiscriminately, and as such I really have no idea what their family trees look like. I don't have much to go on other than their last name, which is a imperfect metric at best. Not infrequently I'll put two dwellers into living quarters only to find out that they're considered related. How does the game determine whether or not two dwellers are related?

This question is largely academic, since I haven't been keeping records of who had reproduced with who, but I'm still curious.

  • 5
    Related question Commented Aug 25, 2015 at 16:29
  • Oh, that question has changed quite a bit since I last looked at it. This might be a dupe. Commented Aug 25, 2015 at 16:31
  • Ah, I knew we had a question like this already. Good find @JonathanDrapeau Commented Aug 25, 2015 at 16:33
  • An answer stating what counts as a family "reunion" between 2 dwellers (dweller with a parent, dweller with grand-parent, dweller with sibling, etc) would answer both questions but so far, none of the answers state the exact nature of those "reunions" or has a complete list of them. Commented Aug 25, 2015 at 16:33
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    I define this question as "what counts", and the duplicate as "can it happen". While an answer to question 2 with enough relevant information could answer this question, I do not agree the are duplicates. They could perhaps be merged, so that a single answer would exist, as @JonathanDrapeau says.
    – user106385
    Commented Aug 26, 2015 at 18:06

4 Answers 4


Game records within each dweller who are his/her parents, and their respective parents. When you try to pair up two dwellers, it'll check if they're related this way. It'll check too if they don't have the same parents. Otherwise you can breed your dwellers as you like. You can pair up a dweller with his/her grandchild's wife/husband for example.


As far as I've been able to determine through my own experience, and what I've read else where, if the people are within three generations of each other it counts as "family." The only exception to this rule is that aunts and uncles can get freaky with their nieces and nephews assuming there is no direct relation somewhere up the family line.


The game determines that two dwellers are related (siblings) if they both have the same set of parents (mother and father). You can still mate a half-brother/sister pair, but can't mate siblings, or parent/children. After a while it becomes very difficult to determine because as you said, the names are not a valid metric (the last name of the child seems to be a 50/50 selection of one of the parents. I admit I've not bothered to keep track enough to see if a dweller would mate with their own grandparent.


You are able to breed half siblings and uncles and aunts and nieces and nephews. I have bred about 50 dwellers with 2 fathers and multiple women, so I have had a lot of cross family relations. One time I was able to breed a grandfather and a granddaughter, but only once. I also tried to breed a great grandfather and great granddaughter, and it worked 3 times.

If you want to keep family trees, do what I do and write it down on paper. It will say if they are related and can not mate if they say its good to hang out with family etc. If they can mate they will start saying romantic things or romantic puns

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