Cationic liposomes have been extensively studied from the experimental and theoretical standpoints, motivated both by their fundamental interest and by potential applications in drug delivery and gene therapy. However, a detailed understanding of the nature of interactions within mixed bilayers containing cationic gemini surfactants is still lacking. This work focuses on the structural and dynamic properties of DODAB membranes in the presence of dicationic gemini surfactants. A thermodynamic characterization of the phase transitions in the mixed systems has been carried out by differential scanning calorimetry, while insight into the molecular interactions in the bilayer has been provided by molecular dynamics. For this purpose, variations in the gemini spacer and tail length, as well as in the respective molar fraction, have been included in both experimental and simulation studies. The results indicate that the influence of cationic gemini surfactants upon the thermotropic behavior and degree of order of DODAB structures is controlled by a complex interplay between charge density, conformation and hydrophobic effects, for which a detailed rationale is provided.