Sounds more like a round worm. Tape worns would be small and flat because they are segmented and come out in peices. If one cat has worms you will probably have to treat them all, but don't panic that today is a holiday. One day will not matter all that much. (I know......waiting is HARD) Try not to go out and buy an over the counter wormer, it is so much safer to just get the "good" stuff at the vet.
Sorry about poor Sky, but don't worry so much, it is a very common occurance. Biddy had worms when I got him. We treated him before he met the other cats but they were so resistant that they survived and I ended up treating EVERYONE!!