Scarlets Head Performance Coach Nigel Davies said: "Simon and Stephen both have great experience and leadership skills on and off the park which they'll now develop even further.
"I think it'll be great for both of them - they have complete respect from all the Scarlets players, who will do whatever it takes to achieve success for them on the field."
Easterby, a former Ireland international said: "I'm delighted to be captain once again - the Scarlets have an outstanding heritage and we're working hard to ensure a fabulous future.
"With the new stadium starting to look incredible, these are exciting times at the Scarlets."
Stephen Jones added: "I'm thrilled to be given the vice-captaincy. It's a real honour and a task I'll take very seriously. We've made some superb signings this summer, Parc y Scarlets is going to be brilliant and we're eager to give Scarlets supporters a lot to shout about."
The Scarlets are due to move to their new £23m Parc y Scarlets complex in November, ending almost 130 years at Stradey Park.
Big name signings this summer have included international forwards David Lyons (Australia), Kees Meeuws (New Zealand) and Simon Maling (New Zealand).