Left-back Barbrook, 20, has joined Chelmsford City, while New Zealand U20 international keeper Gray, 19, will move to Braintree Town.
Chelmsford boss Robbie Simpson said of Barbrook: "Harry probably knows Chelmsford better than many other loan players or players at other clubs.
“He is the twin brother of Finley who was with us last year and came to plenty of the games to watch.
“He is someone who we’ve spoken about bringing in previously. He has spent the first half of the season on loan at Lowestoft Town and has done really well, it was his first proper run of games in men’s football back-to-back.
“He played at left back and at centre-back to a really high level and he is definitely ready to step up to this level and go on even further than that.
“We are delighted to bring Harry to the football club, we know his attitude is going to be exemplary, we know he is going to buy into what we are about and he will add to our options in defence and make us a real stronger unit there.”