don't need to sent brand explicitly in another function you can do it like this:

function Greet() {
    const brand = "Ford";
    const welcome = <div>
        <Welcome name="World" brand={brand}/>
    </div>
    return welcome;
}

and you can also return jsx directly

function Welcome(props) {
  return (
    <p>
      <h3>Hello {props.name}</h3>
      <h3>My car Brand is {props.brand}</h3>
    </p>
  );
}

function Greet() {
  const brand = 'Ford';
  return (
    <div>
      <Welcome name='World' />
      <Welcome brand={brand} />
    </div>
  );
}

that the actual way of doing it

You're getting that output because you're calling your "Welcome" component twice, once with the "name" property and once with the brand property, so the first render is: 'Hello world!! My car Brand is [undefined because you didn't send the brand property] ' and the second rendering is : 'Hello!! [undefined because you didn't send the name property] My car Brand is Ford',undefined values are represented as blank spaces, to get the output you expect you should only call your "Welcome" component once with both properties like this:

<Welcome name={"World "} brand={brand}/>

I hope it helped you, and it's better to send JSX directly.