Term for someone who does more for strangers than family for friends
Solution 1:
Theoxeny I recall this term from Greek mythology, but I don't know of it equates to love of strangers compared to family
[1]: http://Xenia (Greek: ξενία, xenía, trans. ... Theoxeny or theoxenia is a theme in Greek mythology in which human beings demonstrate their virtue or piety by extending hospitality to a humble stranger (xenos), who turns out to be a disguised deity (theos) with the capacity to bestow rewards.
Xenia (Greek) - Wikipedia
What the OP describes is an extremely common psychological phenomenon. I'm interested if there's a more specific answer.