Is it permissible to offer expiation for an oath (kaffarat al-yameen) by fasting specific days in the event of breaking it, and what is the maximum number of oaths for which expiation may be offered?

You are not obliged to fulfill these oaths, and an expiation for an oath suffices you. If you repeated an oath regarding one matter and then broke it, only one expiation is required. However, if you swore an oath, then broke it, then swore another, then broke it again, then you must offer an expiation for each time you broke an oath. The expiation for an oath is feeding ten poor people, or clothing them, or freeing a slave. If you are unable to do that, then fasting for three consecutive days, based on His (Allah's) saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten poor people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days." One should avoid excessive swearing of oaths. The cure for obsessive whispers (waswas) is to ignore them. And if the oaths were made involuntarily, then nothing is incumbent upon you.