The reason for the question is that OP implicitly goes a step too further while identifying "aromatic" limiting forms.
This is of course quite natural, as we treat a limiting structure that is compatible with Huckel aromaticity as aromatic, ie we all more or less consciously or not replace three double bonds with a delocalized ring of electrons.
However not one individual limiting form is aromatic, each can be at most an aromaticity descriptor. In the example given, saying that a) and iv) are aromatic, although sensible, is logically incorrect, or at least involves the reasoning I have described above.
They are certainly important limiting forms as their linear combination stabilise the molecule which will therefore be more or less aromatic. But a mesomer cannot be aromatic by definition.*
I do not enter into the correctness of the antiaromatic part of the question, see comments above pointing to the fact that there is none.
Antiaromaticity is indeed confusing as for it should be taken as a rule for what
it does not happen.
However, this means that limiting forms leading to an antiaromatic flat system will have no weight or contribute marginally.
The concomitant occurrence of sensible limiting forms leading to aromaticity or formal antiaromaticity is not possible within the same flat cyclic system, as it would require a different number of electrons, so at least this point does not need to be discussed :)
*of course in a big molecule we can treat a far away, not resonating group as aromatic, but by doing this we implicitly account for all mesomers leading to its aromaticity.