Articulated bus
It would carry passengers in a trailer/trail vehicle. For example, in Army Basic Training, trainees are often transported in gooseneck trailers towed by Class 7 trucks. Were these allowed on public roadways, they would require a Class A with passenger endorsement (and the road test portion of the Passenger test would have to be done in a passenger transport vehicle which required the operator to hold a Class A CDL).
At a minimum, a Class C Commercial Drivers Licence with Passenger endorsement and no air brake restriction (if the vehicle is equipped with air brakes). If the vehicle has a GVWR of over 26,000 lbs (which is a bit unlikely with an 18 passenger vehicle), then a Class B CDL would be required, again with the Passenger endorsement and without a restriction on air brakes, if the vehicle were so equipped.
All you have to do to get the endorsement is pass the written test and road test in a passenger vehicle. However, if you have a Class A CDL and road test in a vehicle requiring only a Class C CDL, you'll be restricted to operating passenger vehicles in that class and lower.
Take and pass the written passenger test, and do a road test in a passenger vehicle. If you take your road test in a bus under 26,000 GVWR, you'll be restricted to passenger vehicles requiring a Class C CDL. If you take your road test in a single vehicle over 26,000 GVWR, you'll be restricted to operating passenger vehicles requiring a Class B or Class C CDL. You're really not going to find any Class A CDL passenger vehicles.
You have to take the written test, and take a road test in the appropriate class of passenger vehicle. If you have a Class B CDL, but your road test is in a vehicle requiring only a Class C CDL, then your endorsement will come with a restriction limiting you to Class C passenger vehicles. If you're trying to get endorsed for a school bus, a criminal background check is also required. The DMV can tell you how to go about doing this.
Neither. It's a minivan - something distinctly different from either class of vehicle.
If the officer can articulate a reasonable suspicion that supported a vehicle search of the vehicle and occupants then it was valid and legal. Your evaluation of un-suspicious passenger bahavior may be entirely different than that of the officers.
That depends on what the Gross Vehicle Weight Rating of the tow truck is. 26,001 lbs. and up in a single vehicle requires a Class B CDL.
Depends on the GVW of the vehicle. If it's under 26,000 lbs. GVW, it requires a Class C CDL with passenger endorsement. If it's over 26,000 lbs. GVW, it requires a Class B with passenger endorsement.
You may only have one license. If you have a Class A CDL, you can operate a vehicle requiring a Class B or Class C CDL, so long as you have any endorsements necessary for the vehicle type (e.g., tank endorsement for tank vehicles, passenger endorsement for passenger vehicles, hazmat endorsement for vehicles hauling hazardous materials, etc.).
Take the written passenger test, road test in a bus. The only passenger vehicles I've ever seen requiring a Class A CDL were the 'cattle cars' when I was in Basic Training, and those might have fallen under an exemption from requiring a CDL... you'll be restricted to whatever class of license is required for the passenger vehicle you'll road test in, so, if you take it in a bus requiring a Class B, you'll be restricted to passenger vehicles requiring a Class B or C CDL.
Written passenger test completed and passed, road test in an appropriate class passenger vehicle completed and passed.