Toward the end the male aliens are in their alien form during the day while the female aliens and Dr. Smith (with the ring on) are in their human form. The male aliens only turn to their natural form at night so they should be human during the day.
When Non enters the Jupiter 2 to tell Dr. Smith that she didn't sleep well the night before, her shadow can be seen on the fake outdoor background as she approaches the ship before entering.
Even with Dr. Smith activating the landing beam the aliens should not have been able to land as Prof. John Robinson had activated the force field and stated that would prevent them from doing such.
While it is plausible that when packing for a trip through space that the Robinsons included gaming and exercise equipment for their own well being on Alpha Centauri, but it is ludicrous that a cash register would have also been included.
When the 2 male aliens are coming down the elevator in the Jupiter 2, Will looks out from his bedroom doorway. He appears to be looking straight out of his doorway at them, but the elevator is on the same wall as his bedroom, so he couldn't have been looking at them from that vantage point.
When his father comes back after his trip, Will tells him about the horrible looking creatures/aliens that came into his bedroom. Will couldn't have seen them from where he was standing on the top shelf in his closet when they came in.