As stated in the title and description. Have set up PR group with 2 accounts.
Have created a workflow so that when work is added these accounts are notified for approval. I login as the same user and add content to test the mailing.
I received an email as expected … but so have other administrators and another user not related or part of the group hierarchy ??? Please help 
The only people who should receive notification are those members of the group at each step in the workflow schema. Can you post a screenshot of the workflow schema itself, perhaps?