Atomically-engineered heterostructures constitute excellent model systems to investigate fundamental structure-property relations in transition metal oxides and their evolution as the thickness of the constituent layers is reduced to only a few unit cells. The double-perovskite RE2NiMnO6 (RE= rare earth) family is characterized as being insulating ferromagnets, an unusual combination of properties. Ferromagnetism arises through oxygen-mediated superexchange in the rock salt-ordered Ni/Mn sublattice. The Curie Temperature of La2NiMnO6 is Tc=280K, and for the other members of the family, Tc decreases linearly with the size of the ionic radius of the RE. Here, we will show that epitaxial RE2NiMnO6 films (RE=La, Nd, Sm), grown by off-axis RHEED magnetron sputtering, display long-range Ni2+ and Mn4+ order and strain-independent bulk-like TC at a thickness of 30 unit cells. We find that the ferromagnetic behavior occurs down to ultra-low thicknesses of (at least) 3 unit cells (~1.2 nm). However, below 10 unit cells, the magnetic properties deteriorate due to an interfacial charge transfer caused by the polar discontinuity at the RE2NiMnO6/SrTiO3 interface. For the case of Nd2NiMnO6, a detailed x-ray magnetic circular dichroism (XMCD) study allows us to separate the magnetic components into a robust ferromagnetic Ni/Mn sublattice and a paramagnetic Nd sublattice. We will also present our latest efforts in combining different RE2NiMnO6 double perovskites into potential multiferroic artificially-layered superlattices.