Jamie and Craig Overton have signed contract extensions to keep them at Somerset for a further three years.
The 19-year-old Devon-born twins both made their County Championship debuts in 2012.
Fast-bowler Jamie enjoyed a successful season this year, which resulted in a call-up to England's one-day squad for the series against Australia.
All-rounder Craig, meanwhile, missed most of the 2013 campaign because of a stress fracture in his lower back.
Both brothers have featured for England Lions in recent years.
Somerset director of cricket Dave Nosworthy said: "As a club we are extremely pleased to have secured these two young diamonds.
"Both Craig and Jamie are very highly rated nationally and as west country lads we are excited to be able help them develop and at the same time to have them performing on the field for us.
"Long-term expectations around these two is high, so it will be key now for them to just keep their feet on the ground and to get the hard yards in."