The structure and magnetism of epitaxial thin-film dysprosium-praseodymium and erbium-praseodymium alloys with the double-hexagonal close-packed (dhcp) crystal structure have been investigated. Short-range atomic and magnetic order have been found for DyxPr1-x with 0.4 greater than or equal to x greater than or equal to 0.05 and ErxPr1-x with 0.2 greater than or equal to x greater than or equal to 0.05. The distribution of the two species within the alloys was established with x-ray and neutron diffraction techniques. The atomic order is complex; the four planes of the unit cell have differing concentrations of constituents. In addition there are occasional clusters within the close-packed planes. The magnetic behaviour was investigated using neutron diffraction. Surprisingly, only short-range order is observed in the dhcp-structure alloys. Magnetization measurements suggest that Dy0.13Pr0.87 exhibits spin-glass behaviour. The roles of the indirect exchange interaction, the dipole-dipole interaction and the crystal field are considered in detail.