1.Just a few years ago ,tomatoes were believed（tomatoes是被相信为 所以用被动语态 a few years ago是表示过去的时间状语 所以用were ）to have magical powers,making people who ate them fall in love.
2.I wanted to ask him for help,but he was sleeping（wanted是过去的事态 想问的时候他睡了正再睡 过去进行时） so soundly that I decided（过去的决定） to do it alone.
3.Mary told me that the witch cut(转述 引语) an inch of the princrss's hair when the princess answering(伴随状语 a question incorrectly.
1.He and his family are going to Beijing for a-ten-day(又连字符的合成形容词没有复数） holiday.
2.The old man must be spoken to politely.
一定要用被动语态的话就只有这样了
不过我觉得不用比较好