It's hard to guess someone's height when you only see them on stage. Last year I saw Rammstein in a small club in Berlin, and I thought they were rather small guys. I would have guessed Till Lindemann being 1,78m. The data I found on the internet says he's 1,90m, and two of them are over 2m tall.
As for Tristania, I met Anders, ุsten and Kjetil after one show at the merchandise shop. Here are my height guesses for them: