The "Volvo" of bike carrier.... yes, this is a compliment. It's well built, solid, got a new sporty image and even comes from the same Nordic country...
Let me give you some background information about the problem with bikes and family. The trouble with kids is that they grow too quickly, and their bikes follow the same path. I used to be able to fit two adult bikes and two small kids ones on the spare wheel mounted carrier without too much trouble. Now we are talking about almost four full size bikes.
The choice of carriers is not great for three and four bike carriers. A lot of them were to be found too "light" to my liking. If I want to invest a fair amount of money in a product I expect it to last a few years.
My other requirement was to have an easy-to-load carrier, for any type of bikes. This means that I could not use any suspended bike carrier as BMX or woman bike frame would be a nightmare to load without adapters.
I set my choice on the Thule EuroClassic G5 909 with the 4th bike extension (ref 9081).

It comes in a massive box that makes you think that you just bought a monster. But assembly was very easy with good instructions
The extension system clips on the 3d bike rail and can be removed when not required. Thule even provides the transparent sticky tape to protect the surface of the rail from the clips.
Features
The bikes are held in place by one strap for each wheel and individual movable clamps to attach to each bike frame. The clamps are spaced to ensure that bikes do not rub against each other. The extension comes with it's own frame holder to secure the 4th bike to the 3rd one.
The 3rd bike clamp as well as the tow ball clamp and the extention frame clamp are lockable which means that it provides a deterrent for the opportunist thief.
I would still advise to use another mean of securing your bikes if you were to leave them unattended for a long time.
The carrier is quite heavy (about 20kg), and one could struggle a bit to put it in place or carry it. It is also bulky and requires some space for storage.
This is maybe the only "bad" point about this carrier. But this is the trade off for having quality equipment.Don't forget that you can load 3 bikes of up to 20kg each on the carrier and 1 of up to 15kg on the extension.

The carrier attach itself to the car tow ball with a one-hand mechanism. You can adjust it to the size of the tow ball with an Allen key. Just ensure it's very tight. When clamped in place you can secure it with embedded lock.
Another good feature is the ability to tilt the whole carrier to allow access to the boot of the car. Just do it slowly when you have four bikes on it as it is heavy.

Obviously, this carrier comes with the full set of lights and a registration plate holder. The whole lot is an integral part of the carrier, making it very smart and not one of those DIY job.
In conclusion, I do not regret my choice, it is maybe a bit big if I only want to carry one bike (I am keeping my light spare wheel mounted carrier for that use), but this is the perfect choice for carrying multi bikes. The other advantage is that the day I change car, I can still use the same carrier as long as I have a tow ball.