On the ‘alerts’ tab in the settings of a list it is possible to select "Specific fields" as a destination type for an alert. This option allows to choose any field of type (multi) person picker for notifications. When an alert is triggered only the selected users (values of these fields) will get notifications. To do that you need to select “Specific fields” as the destination type and save the alert configuration. After that click on the customize action in the parameters column and an overlay with parameters will open where it is possible to set needed destination field(s).