Abstract
Suppose given a nilpotent connected simply connected Lie group G, a connected Lie subgroup H of G, and a discontinuous group I" for the homogeneous space M = G/H. In this work we study the topological stability of the parameter space R(I",G,H) in the case where G is three-step. We prove a stability theorem for certain particular pairs (I",H). We also introduce the notion of strong stability on layers making use of an explicit layering of Hom(I",G) and study the case of Heisenberg groups.