The TmMn 6 Sn 6 - x In x (0.2=<x=<1.6) and ErMn 6 Sn 6 - x In x (0.1=<x=<1.0) compounds have been prepared and studied by powder magnetization measurements. The In-rich compounds (x I n =<0.5 for Tm and x I n =<0.2 for Er) are ferrimagnetic in their whole ordered range with Curie temperatures ranging between 342 and 253 K. The TmMn 6 Sn 5 . 8 In 0 . 2 compound displays a Neel point at 321 K and undergoes a ferrimagnetic transition at 48 K. The TmMn 6 Sn 5 . 6 In 0 . 4 and ErMn 6 Sn 5 . 9 In 0 . 1 compounds display re-entrant ferrimagnetism. They are characterized by a large increase in the magnetization at the ordering point (T~322 and 342 K, respectively), a transition to an antiferromagnetic state at lower temperature (T~264 and 319 K, respectively) and finally by a transition to a ferrimagnetic state at lower temperature (T~111 and 141 K, respectively). In their antiferromagnetic states they display a metamagnetic behaviour (H t =<3.2 kOe). At low temperature all the compounds studied do not display large magnetocrystalline anisotropy. These results are discussed and compared with those related to the RMn 6 Sn 6 and RMn 6 Ge 6 - x Ga x compounds (R=Er, Tm).