is there any way to free up an engine
It sounds like you are on the right track. All you can do is keep putting penetrating oil or diesel fuel down in the cylinders and keep rocking the car. This should break it free if it has only been setting for about 3 years. I have seen cases where water has leaked down in the cylinders and rusted the pistons to the cylinder walls. In extreme cases such as this, you would have to pull the motor down to do some more extensive repairs.