htech says:
It is not possible to help someone that's trying to help. If the spell is an end in itself, ok, we follow the rules above. If not, if it just something to help another roll, it gets very convoluted.
To clarify, if the spell an Amplifico one (which almost always manifest as Assets even if they are the end-goal of a specific casting), and the casters are largely cooperating as equals (and not as the convoluted helper-of-a-helper chains), do they use the 'combine Skills of multiple PCs' principle, or is Amplifico cooperation strictly impossible ('not possible to help')?