__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
Force: Kylo Ren solos. His displays of Force mastery are beyond what we've seen the Inquisitor do in his engagements with Kanan. Rey is the weakest link here, as she hasn't had any formal training in the use of the Force. However, this lack of training is somewhat made up for by her raw power. The GI is skilled and powerful, but both members of the duo have more raw power than him, and Kylo Ren is more skilled.
Sabers: This is where the Grand Inquisitor might stand a chance. Rey is only really trained in staff fighting, and her skill with a lightsaber is raw and unfocused. Kylo Ren has been trained for an unknown period of time by Luke and Snoke, but we know at the very least that he has 11 years+ of experience as a Force user (going by Bloodline). However, we're also not sure how much knowledge Luke and Snoke were able to pass on when it comes to lightsaber combat. The Grand Inquisitor, meanwhile, is familiar with all seven forms, and is fairly skilled at employing them. My guess is, the GI could bring down Rey rather easily, and the real fight would be between Kylo Ren and the GI. That said, Ren might take down the GI due to raw natural talent granted to him by his lineage.
All out: Again, Kylo Ren solos. His demonstrated Force abilities are superior, and his lightsaber skill is likely comparable to the Grand Inquisitor's. Throw in Rey to back him up, and this goes from a close fight to a stomp in the duo's favor.