If I’m the stepdad am I expected to financially support all of her kids?

If I have a child with a woman who has two other kids by two different dads, am I responsible for them because I feel like it should be on the other dads but they both never show up and pick up their kids, they haven’t been there in months, is this gonna all fall on me?

If I’m the stepdad am I expected to financially support all of her kids?
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