Your second question about spacemen from other planets; it is stated in the Vedic literature that there are many planets where the inhabitants are more advanced than the inhabitants of this earth planet. So it is not unlikely that such people may have developed space travelling methods. They occupy higher posts in the creation of the Lord and so they may be considered as demigods in the same way as the president is specially empowered by the nation, but this does not mean that such spacemen are necessarily carrying the messages of the Lord, just as the business of the state employee is not to act as the state representative but he acts in his particular job.
Because Krsna know everyone's future does not remove our free will. Someone may commit a theft, and if I know that then I know that he will be captured and punished. That is knowing his future, but know that future does not mean that he had no choice not to commit the criminal act. There are two destinies for every one. One destiny is in Krsna Consciousness and the other destiny is in material consciousness, so if someone is in Krsna Consciousness then Krsna knows his future and if he is in material consciousness and acting in that way then Krsna also knows his future. In this way the free will is not affected by knowing the future of the living being, that is an erroneous conclusion.