The single TlO layer TlSr2Can-1CunO2n+3 with n = 2, often called Tl-1212 phase can be extensively subjected to elemental substitutions forming numerous superconducting materials in the family. In this paper, materials with nominal starting compositions (TI0.8M0.2)Sr2(Ca1-x Crx)Cu2O7 with M=Bi and In have been prepared and investigated by the d.c. electrical resistance method and powder X-ray diffraction analyses. Most of the samples showed the Tl-1212 as the major phase and 1201 as the minor phase. The Bi-substituted samples showed a higher onset temperature and higher 1212 phase volume fraction compared to the In-substituted materials. The importance of ionic radius of the substituted elements and the effect of melting/volatility point of the starting components on the onset critical transition temperature (Tc,onset) and phase formation is discussed.