Neutron diffraction was used to determine the deuterium sites in TbNiAlD1.28 and TbNiAlD0.8. Both samples were found to crystallize in the orthorhombic Amm2 space group. Our analysis reveals that deuterium in TbNiAlD1.28 occupies positions at x=0 and x=1/2 only, while TbNiAlD0.8 shows the formation of two different phases. For TbNiAlD1.28, additional magnetic reflections are observed below 16 K indicating antiferromagnetic order. On the other hand, at 10 K, only one of the TbNiAlD0.8 phases was found to be magnetic. In addition, our study of the localized vibrations of hydrogen in TbNiAlH1.39 and in its non-magnetic analog YNiAlH1.35 using inelastic neutron scattering supports the existence of two different hydrogen sites in the saturated hydrides.