What would be the sizes of the bodies created from Jupiter's trojans? If all trojans from the Greek camp and all the trojans of the Trojan camp were combined into two bodies respectively, what sizes and masses these bodies would have? Would they qualify as dwarf planets? Would they be greater than Ceres?
The mass of the Trojans (both camps as far as I know) is estimated at around 0.0001 Earth masses (reference) (Note that this number is debated). The density of them vary but the highest found is around 2.5 g/cm^3 (reference) Assuming that the composition is mainly rocky/icy with very little gas, the act of combining all of them should make a rocky/icy object with that mass.

The mass of Ceres is estimated to be 0.00015 Earth masses with a density of some 2.1 g/cm^3 (reference). 

If we assume that the object made from the Trojans has the same density then they should roughly make an object the same size or slightly smaller than Ceres (about 1 % the mass of the Moon). Make that into two equal bodies and you have half a Ceres per group (so each smaller than Ceres) (assuming that there are the same mass of bodies in each group originally).

Given that there is much uncertainty associated with this, I would bet that the mass and size would be smaller than this.
Whether they would qualify as dwarf planets, I'm not sure. But they would have to be captured into the orbit rather than be formed there as I'm pretty sure the gravitational influence of Jupiter would prevent any coalescence and gravitational stability of the Trojans (though I could be wrong on this).