I think it was probably Doholov (spelling?) who killed at least Lupin, hes mentioned as duelling with Lupin when Tonk's asks where he is and then later hes said to be fighting against Dean Thomas, I believe it is. I'm going to guess that Tonks was likley a victim of the same Death Eater seeing as she would have probably rushed to her husbands aid. Seeing as how Lupin was pretty much my favourite character I'm pretty hacked off about that one.
__________________ Yet the making of things is in my heart from my own making by thee; and the child of little understanding that makes a play of the deeds of his father may do so without without thought of mockery, but because he is the son of his father.