Your stepparent’s kids are probably as nervous about you as you are about them.

Nervousness in a blended house is usually mutual and invisible. You are watching them for signs that you are being replaced, and they are doing the same across the kitchen, each reading the other’s awkwardness as dislike when it is mostly fear of getting it wrong. Nobody in that situation chose the arrangement, and all of you are improvising.

If it is awkward, you might go first on one small thing: ask what they are into, offer the front seat, say the obvious joke about how strange this is. Low stakes is the right size. You are not trying to get close, only to stop being strangers.