how to stick bombs, grenades, boulder and fire ball on place?

In some of my crafts, I need to have some grenades or bombs(or both ^^ ) but they don't react like normal blocks: they just roll around without staying where I initially placed them.

Is there a way to make them stick on the block I want, or do I need to do some artificial case made out of block to hold them?

Also: why do the grenades need a whole block between them? once the simulation start they can stand side by side without problems.

Thank you in advance, and sorry if this is in the wrong place, this is the very first thing I post here.
Answer to your first question: use grabbers, which are under "Mechanical". Place a block, then place a bomb/fireball/etc onto the block, then replace the block with a grabber.

Answer to your second question: the collider used for block placing is different from the physics collider.