The text of the circle casting feat says:
You may aid another spellcaster who also possesses this feat,
granting them a temporary +1 bonus to their caster level, as well as granting them access to your spell points and talents as if they
possessed them. You must spend a standard action every round to
maintain this ability, and you must be within 30 ft. of the caster you
are aiding in this manner.
A target may be aided by multiple casters at once in this manner, but
all involved casters must remain within 30 ft. of each other, and the
effects are not strictly cumulative. It takes one aiding caster to add
a +1 enhancement bonus, three to add a +2 bonus, six to add a +3
bonus, ten to add a +4 bonus, and fifteen to add a +5 bonus. No caster
may receive more than a +5 bonus in this manner.
Thus, if you use this feat, and either the caster himself or the aiding caster has Restore Mind, casting cure will heal 2d8+(CL+1), as one aiding caster will increase the actual casters caster level by 1.
Both casters having Restore Mind (or any of the Life Sphere talents) will not grant you an additional 1d8 of healing power, as those talents do not specifically say that they stack with each other, and if that is not explicitly mentioned, it usually is not the case.
The power increase from circle casting, as per the feats description, comes from a temporary CL increase only - that's good for spells where the save DC increases with CL, but not really for damage dealing or healing spells, as the effect is so minute.