I like the new Stephen. He seems to suit the role a lot more than Edward Savage did, and I really like the way he is with the twins, especially Lucy. He seems a lot more grown up than 17, and Stephen didn't seem 12 when he left for New Zealand and was played by Edward Savage.
Jane definitely doesn't know. She might think he's a bit unsettled at supposedly coming back to see the father than brought him up after having such a hard time with his real dad, as Pat said; and to find that he's not actually there. She definitely did have her reservations about him even before he made a pass at her though; Lucy didn't like her much as it is, maybe she feels that with someone around of similar age to that that Craig was, she will be wanting to impress him, too, and feels that Lucy will push her out completely.