Alyson Dixon and Sonia Samuels also guaranteed their marathon spots in Sunday’s race in London.
Dominic King has also been selected for the 50km men’s race walk.
Callum Hawkins and Tewelde, who claimed asylum in Britain after competing for Eritrea at the 2008 World Cross Country Championships in Edinburgh, qualified as the first two Britons to cross the line in Sunday’s marathon.
Hawkins clocked a personal best time of two hours 10 minutes 52 seconds to finish eighth, while Tewelde was 12th in a time of 2:12:57 – both within the 2:14:00 qualifying time.
His brother Derek ran within the qualifying mark by clocking 2:12:57 to finish 14th and has now been awarded a discretionary place.
Dixon and Samuels, who finished 13th and 14th respectively, had already run the qualifying time of 2:37:00 in Berlin last September.
Sunderland runner Dixon tweeted:“Dreams do come true if you believe in yourself and work hard for it. I’m going to the Olympics!!”
King competed for Great Britain in the 50km walk at London 2012.
The selection of the six athletes takes Team GB’s total for Rio 2016 to 53 across five sports, with 11 sailors, four slalom canoeists, six shooters and 26 swimmers having already been selected.