how can i make squishy objects collide with each other?
or is there any other method for creating DOP soft bodies which is not particle based?

Maybe using wire objects can give you what you are looking for ?

If you don't mind giving Houdini 9.5 (which is still in beta) a try, you can simulate soft bodies with DOP cloth by using the “Cloth Object” tool on the “Cloth” shelf to turn a piece of geometry into cloth. If the geometry is closed, it will behave like a soft body. Any collisions with rigid bodies and with other soft bodies will be dealt with by the cloth solver. You can adjust the amount of stretch, bend, etc from the “Physical” tab on the Cloth Object DOP's parameter dialog, or you can paint those physical properties as geo attributes on the surface for finer control.

Because Houdini 9.5 is still in beta, we cannot encourage you to use it in production just yet. However, if you want to explore this alternative for future use, do know that it exists.

thank you claude and cb

i have tried wire object, it worked, very good to know that it is possible to use wire dynamics to closed polygon meshes, however it was very slow with more objects colliding together even with subsampling set to 1

i will try 9.5 cloth, thanks for the info