You need to specify Your problem more detailed, are You talking about two different peaks in one chromatogram (as the picture suggests ) ore are You talking about the same peak in two different runs?

In the first case:

Two different peaks means two different compounds. The response factor of an FID is different for each compound. The response factor depends on the number of "burnable" C atoms in a molecule, for example CH3OH gives a good response but CCl4 is hard to find.

is a solution with seven diferent PCB (1:1:1:1:1:1:1).

Who is the response factor for this compounds?

there is no "list" of response factors as the final response depends not only on the compound but also on the complete method and equipment.

PCB are mostly done with an ECD instead of FID

The different PCB's contain a different number of Cl atoms (2 to 10), the more Cl the lower the response on FID and the higher the boiling point. As the boiling points span a extended range there is also risk of mass discrimination in the injector: if the method is not correct there will be more loss for higher boiling ones

Thanks