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In this we are mainly concerned with the study of (special) 2-parameter envelopes of n-spheres 'M POT.N' (n'MAIOR IGUAL'4) in a simply connected space forms 'Q IND.C POT.N+1' (c=0, 1 or -1) which satisfy the weingarten relation a+bh+ck=o between the mean curvature h and the gauss-kronnecker curvature k of 'M POT.N'SETA'Q IND.C POT.N+1', where a, b and c are real constants, such a relation includes the case h = constant. We obtain some examples of those objects as well some non-existence results. We also study the possibility of a 2-parameter envelope of n-spheres 'M POT.N' in 'H POT.N+1' (case c=-1) be isometrically immersed into 'R POT.N+2' with everywhere zero normal curvature tensor. In our approach, the focal set of the envelope plays a fundamental role in the characterization of the envelope, in the construction of examples and in the proofs of results