Use a scene. If you always want them to be the same value. Then another scene if you want to set them all to different values, this is the simplest way.
Not if you want to change the values. But to have a number of scenes with set values is easy.
You could try something like this for what you want, there may be other blueprints try searching for them. I have not tried this so no idea if it will do what you want or not.
You can also use an entities card with these four numbers and add an action - such as double_tap - to each item (number) on the card, to transfer its value to the other numbers. A script can handle the transfer. This way, you retain the ability to modify each number individually.
alias: Sync numbers
description: >-
The script sets states of the entities listed in **`allNumbers`** to the state
of the entity passed as **`source`**. The source entity must also be included
in **`allNumbers`**.
sequence:
- variables:
allNumbers:
- number.skylight_ne_temp_value_v2
- number.skylight_nw_temp_value_v2
- number.skylight_se_temp_value_v2
- number.skylight_sw_temp_value_v2
sourceState: >-
{{ states(source) if source is string and source in allNumbers else none
}}
- if:
- condition: template
value_template: "{{ sourceState|is_number }}"
then:
- action: number.set_value
target:
entity_id: "{{ allNumbers|reject('eq',source)|list }}"
data:
value: "{{ sourceState }}"
alias: if the state of source entity is numeric
Are the four items showing up as lights/bulbs in Home Assistant at the moment?
If they are, you probably just want to create a light group.
That basically allows you to control the brightness, color temp on/off of all the bulbs as a single entity.
If they are not lights/bulbs and are in fact simply numeric entities (per your post title) then you will have to use one of the other answers here.