According to David Ornstein earlier this week, Southgate will call up Walker, Trippier and James for his RB options.
Regarding TAA, I don't watch international games these days and so, I don't really have a clear inkling on how he fares for England but I wonder if it's fair to argue whether TAA's form/performance is a byproduct of Klopp's system. The way he plays allows the FBs to shine, it makes the FBs as the creators in that Liverpool team. Southgate has a different way of playing and likely views TAA differently, on top of his defensive deficiencies.