Custom notifications for contacts

Automation is the preferred option. Many apps are available. I prefer using MacroDroid , since it is free (upto 5 macros) and easy to learn. To understand how MacroDroid works and required settings, my answer here

Your macros would look like this

• Important SMS (name of macro )

Trigger: SMS Received → SMS from (select contacts) →SMS content (any)

Actions:

1. Vibrate → Select vibration option

   
   
   
   
   
   • Long press on above action and select Add Constraints → Ringer Volume → Vibrate or Silent
   
   



2. . Ringtone Configure → Select Ringtone option

   
   
   
   
   
   • Long press on above action and select Add Constraints → Ringer Volume → Volume on
   
   

Constraints: None

Note: Action 2 not tested, since I need incoming text for that and don't have a device for that