We examine the possibility of existence of dynamical resonances in collinear (He,HD+) and (He,DH+) collisions by analyzing their respective transition state spectra on the McLaughlin-Thompson-Joseph-Sathyamurthy potential energy surface (PES). The spectra are computed by Fourier transforming the temporal autocorrelation function, C(t), of the initial wave packet. Some of the well resolved resonances are analyzed by computing their eigenfunctions and lifetimes. The vibrational state (v) - selected energy resolved reaction probabilities (P-v(R)(E)) for collinear (He,HD+) and (He,DH+) collisions are also calculated on the same PES by computing the reactive flux in the product channel. The P-v(R)(E) values for HeHD+ show a characteristic staircase-like structure that can be related to threshold resonances. The P-v(R)(E) values for HeDH+ on the other hand, are highly oscillatory, in keeping with the densely packed transition state spectrum.