The 6 series, either coupe or convertible, do not have spacious back seats. The seats are for carrying small parcels or your briefcase: not people: at least not people you like.
There are 7 seats in a BMW X-5. There are the driver and passenger seat, the 3 middle seats, and two seats in the trunk. The two seats in the trunk are small and non-spacious, so they may not be considered seats for large people.
You have to remove the top part of your right rear passenger seats the battery is located under.
The 2012 BMW 7-Series has 14.0 cu.ft. of cargo capacity with all of its seats in place.
The 2004 BMW 3-Series has 10.7 cu.ft. of cargo capacity with all of its seats in place.
The 2008 BMW 7-Series has 18.0 cu.ft. of cargo capacity with all of its seats in place.
The 2009 BMW 5-Series has 14.0 cu.ft. of cargo capacity with all of its seats in place.
The 2003 BMW 7-Series has 18.0 cu.ft. of cargo capacity with all of its seats in place.
The 2011 BMW 1-Series has 10.0 cu.ft. of cargo capacity with all of its seats in place.
The 2014 BMW 6-Series has 13.0 cu.ft. of cargo capacity with all of its seats in place.
The 2010 BMW 5-Series has 14.0 cu.ft. of cargo capacity with all of its seats in place.
The 2005 BMW 5-Series has 14.0 cu.ft. of cargo capacity with all of its seats in place.
The 2005 BMW 7-Series has 18.0 cu.ft. of cargo capacity with all of its seats in place.