Is it obligatory to wash the anus and the concha of the ears during ghusl if the person performing ghusl cleaned himself (istinja’) before wudu, and then performed ghusl? And is istinja’ sufficient instead of washing the anus?

If one washes the anus with the intention of performing ghusl (definition) for janabah (definition), that is sufficient. Otherwise, it must be washed again. The more complete way is to first wash the areas of impurity, and then perform ghusl with the intention of ghusl for janabah. As for the ears, their outer and inner parts must be washed, and merely passing water over their openings is sufficient.