If you agree from the observer at rest it will take one year to meet half way then they are traveling at 1.2C. Observer can measure 0.6 and 0.6. The spaceship can't measure 1.2C. That is all light is: a measure.
My point is on non-relativistic notions just as you mentioned. If one spaceship is 1.2 light years apart from a planet, how long does is take for a 0.6C spaceship to reach the planet? 2 years. Now if another spaceship is launched from the planet at 0.6C how long until they meet (collide)? 1...
Only the observer outside the spaceships has this information. No one inside can make this calculation: there are no 2 speeds from the inertial frame of reference of the spaceship.
If you are inside the spaceship, you agree with me you have no information about the relative motion of the two objects? Your measures will probably say it is moving 99.99% C but it will be wrong. The external observer can actually calculate time to impact. Each ship by itself can't.
For the observer inside the spaceship there is no relativity. His frame of reference is inert for every purpose. Nothing to add or subtract. Just unable to measure an incoming ship at 120% the speed of light.
Relativity always talks in terms of observer but fail to explain common sense problems like this. The fact that no one can measure anything faster than light does not preclude to objects moving towards each other at a higher velocity than an external observer can measure. Move the observer to...