No, it doesn't strengthen your point, it weakens it immensely. Because the fact that the child in this case (me) loved non-blood family members as much as my blood ones. It was only those who focused on that point who grew cold, but those close to me still retained their bonds.
It is a self-fulfilling prophecy. You think it will be an issue, so you see it as an issue.
Also, since you now provided information, the children live with their mother. You can feel safe not seeing them as part of your family as they are not involved with your family. If the children were living with your sister, it is an entirely different point.
I did get along with my step-mothers family, but it was nice gestures and hellos. You don't need to go "out" of your way for them, but it might be nice to be at least pleasant towards them.
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