Rotational structures at ultrahigh spin in 157158159Er have been investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. Configurations of observed bands are assigned and the corresponding deformations are given theoretically. The calculations suggest that one of ultrahigh spin bands in 158Er is triaxial highly deformed and the other is normal-deformed, while both ultrahigh spin bands in 157Er are suggested to be triaxial highly deformed. The possible ultrahigh spin bands in l59Er are predicted to be triaxial highly deformed and have shape coexistence in the same configuration. The configurations with two neutron holes in the Nosc=4 orbitals and two neutron holes in the h11/2 orbitals in 159Er are favoured for ultrahigh spin states but unfavoured for band termination, which is similar to ultrahigh spin bands in 157,158Er.