If I understand you correctly you have three sliders.
A change in parent will be sent to childA and childB. A change in childA or childB won't affect the others.
If this is correct you will need to register to the 'Value Change' event of parent.
When the event is triggered you sent the value to childA and childB with a 'Value (signalling)' property node. The value signalling will make sure that 'Value Change' events of the children get triggered as well.
When you move around the slider the children will follow.
Option B when you need the three sliders to always be the same you can do that quite easy with the following steps:
- Place a slider
- Right click, visible items-> digital display
- Right click on the slider -> Advanced -> Customize
- Right click on the digital display-> Replace -> a Slider (child A)
Do the same exercise for Child A
- Right click, visible items-> digital display
- Right click on the slider -> Advanced -> Customize
- Right click on the digital display-> Replace -> a Slider (child B)
Now you have three sliders which always will be linked without any extra code.
Ton