Superconductive 2:2:1:2 phases of the type Bi2Sr2Ca1-yLnyCu2O8+x+y/2, where Ln stands for Yb or Er, have been synthesized and characterised by X-ray and electron diffraction. The small rare earth atoms prove to substitute preferentially in the Ca site. The electrical properties as well as the structural characteristics of these compounds are affected by the rare earth substitution rate. It is shown, in particular, that the long axis parameter of the subcell and the incommensurate period of the modulation decrease with increasing y. The substitution of trivalent cations for Ca requires the presence of additional oxygen atoms in the structure, the location of which is discussed.