Drinfeld realisations are constructed for the quantum affine superalgebras of the series ${rmmathfrak{osp}}(1|2n)^{(1)}$,${rmmathfrak{sl}}(1|2n)^{(2)}$ and ${rmmathfrak{osp}}(2|2n)^{(2)}$. By using the realisations, we develop vertex operator representations and classify the finite dimensional irreducible representations for these quantum affine superalgebras.