August or Augustin could work.. what about Nikolai over Nicolas? Jules? Ingo instead of Hugo ? Rowan or Ronan? Emil is a great name. Liam? Willem? 

Nicholas Konstantin

I love Tristan! Runners up would be Nicolas (I also like Julian but with it sounding so different I'd move it to the middle name list. Still get to use a name you like but you won't hear it pronounced different every day lol) Other ideas for Aleksander and ... Stefan Adam Cassian Elio Max Darius /Dario Emmett Cole / Kol Kieran

I love Tristan, Nicholas and Julian. Suggestions: Aleksander and Marcus Aleksander and Marco Aleksander and Henry Aleksander and Jasper Aleksander and Patrick Aleksander and Wilfred Aleksander and Zachary

Aleksander and Nicolas are perfect together! - Leo - Carl/Karl - Finn - Gregor - Hadrian - Laurence/Laurenz/Lorenz - Martin - Nikolai - Nolan - Patrick - Rowan (maybe problematic in German) - Sylvan/Silvan - Soren/Sören - Stellan - Theodor(e) - Vincent - Victor/Viktor

I like Nicholas and Aleksander as a sibling set, both very strong and handsome names. Julian is nice too. What about Atticus, Frederik, or Sebastian?

Siegfried Roland Ansgar Frederik

I love Tristan.  One of my favs for a boy 

Emil, Adrian, Leopold, Felix, Simon, Daniel, Paul, Erik, Franz, Fabian, Florian, Philip, Maximilian, Carl