The girls took the title at the United Nations Jujitsu Championships, held in Blackpool last month, where 10 nations from across the globe competed.
Both are students at Chelmsford County High School for Girls, with 14-year-old Rheanne in Year 10 and 13-year-old Eva in Year 9.
The girls, who live in Billericay, won a gold medal in the pairs demonstration category, where they had to perform synchronised moves.
Rheanne won a bronze medal in random attack category, where opponents are tested for their all-round awareness, with Eva taking silver.
The girls train three times a week with the Wakarishin Jujitsu Club based in Basildon.
Rheanne said: "The sport is extremely hard work but great fun as well.
"I would recommend anyone to take it up as it is such an enjoyable way to keep fit. It is also fun competing with my sister."