  We address the ferromagnetic tendencies detrimental for superconductivity
that are related to the substitution of the pnictogen As atom with Ge or Si,
together with additional substitutions in the spacer layers in 122 and 1111
Fe-based superconductors. Intermediate compounds in which these substitutions
are realized individually are studied within density functional theory. We thus
single out the control of spacer ions as an effective way to handle such a
ferromagnetism, and we also show that it is suppressed in YFe$_2$Ge$_2$ under
pressure ---which then can be expected to enhance its superconductivity.
