The only thing I could see wrong was number 9 at the very bottom of the page. It should be "may be having a lunch break". Also for number 2 at the top I would use must. On the other hand to me as a native speaker, have to and must sound interchangeable. Where you put have to could also sound right with must. Same with neednt and dont have to. So I'm not sure if there are specific rules for that with this worksheet, but for me the rest all sounds correct!