How to prevent character to walk?

you could overlay the whole scene with a transparent interface. This prevents the character moving but it also prevents that the mouse can hover objects in the scene...

Yes mate, as you say then user cant hover objects.

@ Lee, I'm confused bro for the npc characters. To make a 3d character as npc then I should use an outfit for it. And then what I do is, changecharacter to npc_3d and change outfit. What am I doing wrong? And how I can not set the npc as active character. Because whenever I do changecharacter, then the new npc becomes active character.

I didn't say anything about change character. I said swap the characters, not replace the currently active character.

1. create a duplicate of your playable character. Do not add a start position to it.

2. take note of the current position & direction of the active character or use Lua script to store the current direction & position.

3. send the active character to another scene or to empty.

4. send the duplicate (npc) version of the character to the position where the active character just was & set the correct alignment.

5. play whatever animations of the npc you need it to play when interacting with scene objects (you'll have to use a condition / value or lua script to query which actions should be executed).

6. when you want to be able to control the character again: repeat steps 3 & 4, but in reverse.