I bought some of the animal ones. The single seat cover fits perfectly on my single seat. The double one really doesn't fit! It doesn't come down over the headrests and there's no hole for the seatbelt exit in the middle of the seat.
If you have the same you should find they are a bit stiff to get over the head-rests but they do pull down. Seat belt should be reached through the velcro strip which starts at a point just between the two headrests and runs down from top to bottom. The same applies to the red seat covers.