User blog comment:B214/Volume 22 spoilers/@comment-24552694-20160923205503/@comment-14.201.211.143-20160924001917

Well no devil is born as an ultamite class so the children of them is a high class one (Millicas). Ex is the only one from the future who is known to have at least two high class parents (Ravel left her family so she would have been demoted as she was no longer a Phenex and work her way up like a reacarnted devil) because we do not know if the girls obtained high class in the future.

Another reason for them not having a peerage is they just havn't been given there Evil Pieces yet because Ravel is currently older then when Rias got her Evil Pieces and she hasn't got them, so they could just be waiting on them