It's hard to work out the back row pecking order, and No8 may vary depending on the opposition.
For me, it's something like
6. J.Willis, Shields, Johnson
7. Young, J.Willis, Carr
8. Carr, Vailanu, T.Willis
There's also Morris and probably some others I can't think of
It's hard to believe that Ash is 3rd choice and likely doesn't feature on the bench when all are fit