Just to be clear because it hasn’t been explicitly stated here. The concept of Groups only exists for Items.
The closest thing to a Group for variables is, as recommended here, using a Map or a List to store the variables. Then you can iterate over the entries in the Map or List and do your operations on them as desired.
In JS Scripting I’ve a library that actually does this sort of thing with Timers for you. I’m working on making it installable as an npm and will then see if there is interest in adding it as a part of openhab-js. But with TimerMgr there is a cancelAll() method with will cancel all the currently existing timers handled by the manager. Null timers would not exist.
I posted the code for TimerMgr at Some JS Scripting UI Rules Examples which might give you some ideas for how to handle manage the book keeping involved when using a Map for this in Rules DSL. See Design Pattern: Working with Groups in Rules for how to filter and otherwise manipulate Lists in Rules DSL (a Group’s members is just a List.).