Martinez told reporters: "We have a good relationship and a professional relationship and I want to believe that they feel that they can trust us in sending players out on loan.
"I don't think that relationship goes any further.
"[The chairman] has developed that bridge between the two clubs and there is a possibility for both to use it in a good way, but there is no commitment in any sort of future deals."
Barkley, 20, came through the Everton youth system and has since had loan spells at Sheffield Wednesday and Leeds United.
Stones, 20, was a product of the Barnsley academy and joined Everton in 2013 after making 24 appearances for the first team.