The pertinent rules...
Fire Lash is a Psi-like Ability that conjures a one-handed whip of fire as a move-equivalent action, which remains as long as its creator holds it.
Weapon Afire, and later Greater Weapon Afire below it, are also Psi-like Abilities that add 2d6 fire damage (which becomes 4d6 with Greater Weapon Afire), as a move-equivalent action, to a weapon. The effect continues as long as the weapon is wielded by the pyrokineticist.
The Multiple Effects section, along with the Stacking Effects immediately below it have this to say:
Powers or psionic effects usually work as described no matter how many other powers, psionic effects, spells, or magical effects happen to be operating in the same area or on the same recipient...
Powers that provide bonuses or penalties on attack rolls, damage rolls, saving throws, and other attributes usually do not stack with themselves. More generally, two bonuses of the same type don’t stack even if they come from different powers, or one from a power and one from a spell. You use whichever bonus gives you the better result.
So, the fire lash is not a bonus to the same target, the whip produced is the effect of the power, and each whip is an independent effect. Thus with 4 move equivalent actions, and 4 hands capable of holding the whip, a pyrokineticist can produce 4 flame lashes. Penalties for attacking with multiple one-handed weapons would apply if the pyro attacked with more than 1 in a given round.
Weapon Afire, later modified to Greater Weapon Afire, is a bonus or modifier applied by a power, so its effects may apply only once per target. Thus, with 4 more move-equivalent actions, a pyro already wielding 4 weapons can enhance each of them with this ability, lasting as long as the targeted weapons remained held.
The Fire Lashes are legal targets, because they're weapons that the pyro is holding, by definition. Each Fire Lash under the effect of a Greater Weapon Afire would deal 1d8 fire damage plus 4d6 fire damage on a successful ranged touch attack. Each could be potentially be disarmed, ending both effects simultaneously.
Refer to said girallon arms question to determine whether it's effective in allowing the wielding of extra weapons.