Beginners, some click game issues, monster generation failure/collision invalid, etc.

[winter rampart]

Hello! I am a beginner. I studied mob_scene: PackedScene according to the official DOC. I encountered the following problems and hope to get some help.

Situation: I'm making a point and click game, and monster MOBs are queued up (from left to right).
In the convenience store, the player has to wait for the MOB to go to P1, press the button, and the MOB will move to P2->P3->P4>FREE

The following is the problem I encountered

1. My MOB is generated in MAIN, but it can only generate one, (together with the MOB originally in MAIN, there are 2 MOBs in total). How can I generate many MOBs according to time?

2. I wrote INPUT detection in the MOB script. When I generate and press the keys, they all react together. How can I control only the MOB on P1 to react?

3. There need to be only 2 MOBs, but when they queue up to go to P1, the second MOB will squeeze P1 out of the BLOCK. Although my BLOCK already has a collision effect, it is invalid and the MOB is still squeezed out. What should I do? manage?

4. I have a UI, which is a pink progress bar, showing the anger of the MOB, but the newly generated MOB has a layer above the UI. How can I control the UI to always be at the top?

This is my code to generate the MOB, MAIN.GD

extends Node

@export var mob_scene: PackedScene
@onready var mob = mob_scene.instantiate()

func _ready():
    pass
    
func _on_buyitemhere_bye():
    if Input.is_action_pressed("R"):
        print("noonehere")

func _on_yjhcometimer_timeout():
    mob.position = $p4.global_position
    add_child(mob)

func _process(delta):
    _on_buyitemhere_bye()