What is the ruling on someone who performed Umrah and forgot to shorten his hair in the first Umrah, then repeated the same mistake in the second Umrah a year later? Is he required to offer a fidyah (expiation)? If so, is it one sacrifice or two sacrifices?

Shaving or shortening the hair in 'Umrah is an obligatory rite. If you have not yet exited the state of ihram, you must remove sewn garments and avoid the prohibitions of ihram until you shave or shorten your hair, even if you are in your own country. As for any prohibitions committed during that period, nothing is required for one who forgot or was ignorant. The second 'Umrah is considered void because you were still in the state of ihram from the first 'Umrah.