The question tags for your examples would usually be:
1) He had lunch, didn't he?
2) They must know it, mustn't they?
3) They had to go home, didn't they?
Other tags may be possible in some cases but the examples above are the most likely ones. Please see the following page for more help on tag questions and question tags:
http://grammar.englishclub.com/verbs-questions-tag.htm
