No. Sorry. No.
Having just been through this, the buses were an absolute necessity as the parking was just not enough and way too far away. Here in Seattle, the parking area our circuit was assigned to was 1.3 miles away. Friday morning, the traffic was horrendous as the backup was over 2 hours long for some people. They didn't make it to the convention site until 11 or 11:30am, well after the convention started. Lots of congregations hired buses themselves and each person who wanted to take the bus paid for it (plus driver tip) themselves. WTBTS had no involvement in hiring buses, except for the school buses they used for shuttling people from the far parking lots to the site. And each congregation came up with their own "rules" as to how to organize the buses. There was no rule from WTBTS about not riding with family from other congregations. That would appear to be a rule local to your congregation. Although it makes sense because the price of the bus would probably be split by each person riding as it was in several congregations that I'm aware of, and prices varied from bus company to bus company. I know of a congregation that was two hours away from the site that only cost $20 per person to ride. But the bus company our congregation used where we are less than an hour from the site charged over $50 per person. It all depended on the bus company. Some congregations hired school buses, whereas most hired charter buses (way more comfortable).
Why was the parking so terrible? One elder told me that the Huskies normally paid the city over $100,000 per game to close down the streets around the stadium to help with traffic flow. WTBTS didn't do that, so traffic was a mess. Another factor is that one of the big parking lots was closed down to normal parking and reserved for the buses. Another factor is that WTBTS didn't pay for ALL the parking available around the stadium. There were lots that are normally used for other things that would typically be available during a game (for a fee), but WTBTS didn't pay for those, and attendees weren't about to spend the money on them for three full days. That would be expensive for normal families.
There is a problem for football games. Don't kid yourself there. A non-JW told my wife that when they went to a game, they had to park far away, and the walk in was really long. The difference is that people who go to football games are generally willing to put up with that because it's for one day, not three, and they're in much more comfortable attire for walking, and they're not dragging bags of books, food and for the most part, small kids/babies with them. Oh, and non-JWs don't complain nearly as much about this stuff as JWs do. Go figure.