Dear Anon,
You are not what we would call a 'blood' relation...you are related by marriage. Also you might be called, in the vernacular, shirttail cousins.
But relationship is mostly in your heart anyway...if you feel like these are cousins to you, then yes by all means treat them like family!
Legally or biologically you are not related. In my family though we consider everyone extended family. With divorces and remarriages and step-children, and half-siblings the definition of family has been expanded to include a lot more. If you feel they are, they are family.
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