The only legitimate concern in this is the element Tin (Sn) which has an extremely low melting point compared to the other two elements (Cobalt and Iron) so it evaporates relatively easily so it may be tricky (but not impossible to make alloy with the stoichiometric ratio of elements. Secondly, you may want to investigate the miscibility of Sn which is generally a Beta phase forming element (and metalloid) and its solubility can be of concern. Lastly, do brush up on knowledge on how to thoroughly clean your metal elements before melting.