Adam,
When I Direct Add to a subgroup the members are receiving two
notifications, one that a moderator has added them and one that
appears generic.
The "You've been added" notice cannot be avoided. You can add your own text to it, but you can't edit the boilerplate or turn it off.
The other is likely to be your group's Welcome notice. There is a default Welcome notice for each group, but you can edit it as you please or make it not Active (if not Active it is not sent). See the Member Notices tab of your group's Settings page.
See also:
/g/GroupManagersForum/wiki/Member-NoticesShal
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