Single crystals of four novel uranyl selenate and selenite-selenate oxysalts with protonated ethylamine molecules, (C2H8N)2[(UO2)(SeO4)2(H2O)](H2O) (I), (C2H8N)3[(UO2)(SeO4)2(HSeO4)] (II), (C2H8N)[(UO2)(SeO4)(HSeO3)] (III), and (C2H8N)(H3O)[(UO2)(SeO4)2(H2O)] (IV) have been prepared by isothermal evaporation from aqueous solutions. Uranyl-containing 1D and 2D units have been investigated using topological approach and information-based complexity measurements that demonstrate the evolution of structural units and the increase of topological complexity with the decrease of H2O content.