they are different. 生命 means: life; being;existence of an individual human being( or other things) for example:There is no life on the moon（在月球上没有生命） ------ 人生 means: activity of a life ,the interval of time between birth and death. for example:As we know,life is often compaed with a voyage.（正如我们所知，人生常被比作航海） ------ 生活 1,as a verb,means : live, get along For example:After she died, he had nothing to live for.（她去世后，他便失去了生活的目标） 2,as a noun,means : livelihood,life （different from 生命,here life means human existence, relationships, or activity in general:） For example: I prefer country life to city life（我喜欢乡村的生活，不喜欢城市的生活） Have to say,Chinese is difficult for a learner whose mother language is Indo-European language.Believe yourself, you can learn Chinese well.加油~

他原以为他的“人生”会一直这样惨淡下去，然而有一天，她出现在他的“生活”中，他的“生命”都被她点亮了。 No matter what, I will survive the tough times 无论如何，我必将安度这段艰难的时光。

生命：it is used when we talk about living things，like a flower，an animal，a people，they all have lives. 生活：it talks about daily life of people，such as working，entertainment，sleeping and dying. 人生：i think it is more formal than 生活，it feels like more poetic and almost the same meaning of 生活.But it includes more. And i think you can take it like：i am alive（生命）and i had my life（生活），they underlie my lifetime（人生）

life is not easy. 生活不易。加油！