Genetically? No... But Cream and Sonic appear in the same games like sonic heroes and sonic advance, but they are not cousins or anything.
Cream the Rabbit
No. Cream is 9 and Sonic is 23. That's as crazy as Taileam or Shadamy.
Cream the Rabbit's father is Vanilla the Rabbit. Cream and Vanilla are often seen together in the Sonic the Hedgehog series.
Sonic the hedgehog,
Her friends are Sonic the hedgehog (brother), Silver the Hedgehog (brother), Shadow the Hedgehog (brother) and Cream the Rabbit (close as sisters).
No, Cosmo's mother is shown in Sonic X. Sonic the Hedgehog's mother appears in Sonic Underground.
No, he was always a hedgehog and always will be.
There are a lot of good guys in the Sonic series, so I'll only list the main ones: Sonic the Hedgehog, Miles "Tails" Prower, Knuckles the Echidna, Amy Rose, Cream the Rabbit, Silver the Hedgehog, and Blaze the Cat.
Cream the rabbit out of Sonic can fly with her ears.
Rabbit
Sonic just likes cream as a friend, so no.
Sonic Mega Collection (1 day later, Sonic Advance 2).