My great great great great grandfather is Marko Miljanov Popović, born in Medun, Montenegro 1833. His father was Miljan Jankov Popović. Marko Miljanov is famous so I searched for him on wikipedia. I found it and I also found his great great grandfather Martin Popović's site. There it says that his grandson was Janko Popović. That inscription is blue colored so it's a link. But, when you press it, it takes you to new site "Cincar Janko Popović". I'm not sure are they the same person or is it a mistake. Life years and name fit, but birthplace, life residences and deathplace don't. Also, in whole text it never says anything about Marko or Miljan or about they're Kuči tribe.
P.S: Sites what I was talking abut are on serbian wikipedia.