Are they deliberately lying or do really believe what they are saying ?
They do lie, but reason that it is for your own good I suspect. It is kinda like when Satan told Eve that she would not die, even though God said she would if she ate the fruit. He probably reasoned that it was for her own good so she could escape the horrible evils of the garden of eden and experience the beauty of slavery to sin and death.
Similarly, when Jesus offers his covenant for the removal of sin and it's penalty death in Mt. 26:27,28 the Governing Body explains to everyone that Jesus's wasn't talking to you , just them. They get to be declared righteous and have immortality, but everyone else has to work for it the rest of their natural life and 1000 years in the Millennium to get it.
"And whosoever will, let him take the water of life freely."