Fluid like collision

Hello
I like to make a collision what is similar to the water.
Red color is the real collision and the blue color is a force like collision.
1. when the blue boxes only collide then nothing happening
2. when the blue box and an another red box collide then the red boxes slowly start to push back from each other (some vector math to calculate the push back velocity)
3. when the a red box forcefully bumping into the another red box then it start to push the another red box
This is my idea but i dont know where have i start it. Can you help me? :)