Qadha and fast expiation

[Msilol]

Salam

I must know how Qadha prayers a performed. If you have a lot of prayers to make up do you pray these seperately from the fard, like after asr prayer another duplicate? Can it be achieved by sunan prayers, with multiple intention as voluntary and any forgotten prayer?.

For fasting expiation: If fasts are broken, but the person kept them and did not learn its nullified, should the person make up for it as average? Read it should be a 15 Sa' of feeding the poor for expiation, what can the person do if not possible?

Does fasting 2 consecutive months mean you cannot take a break, for example haydh? Does 1 broken fast (uninentional) equal to 2 consecutive month each or overall?