I think your family just sucks wet rabid dogass.
No need to treat children differently based on their conception.
And yes, children are sponges so you've obviously absorbed their negativity all this time.
For me its the opposite, I'm usually worried that it looks like my daughter gets special treatment and that her cousins will resent her for it, but my siblings have assured me their girls all understand and are supportive of their support.
I'm really sorry you were born into such a cruel and thoughtless family.