This is a simple example of a shared viewmodel

SharedViewModel.java

class SharedViewModel extends ViewModel {

public MutableLiveData<String> liveData = new MutableLiveData<>();

}

class parentFragment {

sharedVm = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);

 sharedVm.liveData.observe(this, new Observer<String>() {
            @Override
            public void onChanged(String stringValue) {
                myTextView.setText(stringValue);
            }
});

}

class childFragment1 {
sharedVm = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);

sharedVm.liveData.setValue("text1");

}


class childFragment2 {
sharedVm = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);

sharedVm.liveData.setValue("text2");

}