The HfFe 6 Ge 6 -type TbMn 6 Sn 5 . 8 Ga 0 . 2 , TbMn 6 Sn 5 Ga, HoMn 6 Sn 5 Ga and HoMn 6 Sn 5 In compounds have been studied by magnetization measurements and powder neutron diffraction experiments. All four compounds are characterized by in-plane moment direction at room temperature. Below 280 K, TbMn 6 Sn 5 . 8 Ga 0 . 2 undergoes a spin reorientation process with the moments aligned along the c axis at 2 K, whereas in TbMn 6 Sn 5 Ga, the moments remain in the (001) plane in the whole temperature range. The HoMn 6 Sn 5 Ga and HoMn 6 Sn 5 In compounds display a moment reorientation process below 175 and 188 K, respectively, and at low temperature the moment direction deviates from the c axis by θ F =61 and 43 o , respectively. The results are discussed and compared with the magnetic behaviour of the TmMn 6 Sn 6 - x Ga x and TmMn 6 Sn 6 - x In x series. All the data suggest that a change of the sign of the A 2 0 and A 4 0 crystal field parameters occurs in Ga-substituted compounds while no variation is observed in the In-substituted compounds. This conclusion should be related to the different distribution of the Ga or In atoms on the Sn sites of the HfFe 6 Ge 6 structure.