Iron germanides and gallides form a diverse range of compounds with various crystal structures, from ordered solid solutions based on different iron modifications to complex monoclinic structures with numerous crystallographically independent positions. Consequently, these compounds exhibit a wide range of physical properties, including magnetostriction and non-collinear magnetism, as well as the unusual semiconductor-type conductivity characteristic of intermetallides. The presence of the isostructural compounds Fe₆Ge₅ and a-Fe₃Ga, allows us to investigate the influence of the p-element on the structure and magnetic properties of these intermetallides in detail. This study characterises these compounds in detail, obtaining for the first time their derivatives of the general composition Fe_6-y(Ge_1-xGa_x)_5+y: T₁ (x = 0.6-0.9, y = 0) and T₂ (x = 0.3-0.6, y = 0-0.12). Their crystal structure and magnetic behaviour are presented and discussed.