Died whilst having fasts of Ramadhaan to make up

My father died after an illness which prevented him from fasting half the the month of Ramadhaan, and he had requested that I [make up the missed] fasts for those days. So am I required to do that or can I make an expiation [on his behalf]?

Broke fast whilst cloudy thinking sun had set

If the sky was cloudy and the mu.adhdhin called the adhaan and [then] some of the people broke their fast based upon [hearing] the adhaan, and after breaking the fast it became apparent that the sun had not set, what is the ruling regarding the fast in this situation?

Intentionally broke fast and then had sexual intercourse

Regarding a man who intentionally broke his fast in Ramadhaan, then had sexual intercourse [with his wife]. Is he required to make up [the fast] in addition to making an expiation, or is he just required to make up [the fast] without making an expiation?