I'd suggest checking your owner's handbook initially. That should tell you the max noseweight of any towbar / equipment on your vehicle.

Isn't the idea to ride the bikes rather than have the bikes ride you?

And what with the electric bit, you'll never get fit on one of those.

;)

One idea is to strip the bikes of as much weight as possible before loading them on the carrier, in particular the heavy batteries. The electrical contacts should then be masked off with tape to stop them getting covered with muck.

Most V40s seem to have a 75Kg towball limit, so you should be fine.

Make sure the bike rack has a number plate and lights, and you should be fine.

If you're carrying heavy bicycles, you will probably find a removable towbar unsuitable; this is because the weight that you can carry (downwards load) can be quite low; on my last car I had a removable Westfalia towbar, and I worked out that I could only carry three bicycles once I had worked out the weight of my Thule cycle rack and the bikes, and even then it was virtually on the limit - the rack is surprisingly heavy!

I only found out about this limitation after I had the towbar fitted; but for this reason on my current car I have a non-removable Witter towbar which gives me more flexibility, though you would need to workout the total weight of the bikes and the cycle carrier to ensure that everything is within the acceptable range.

Having tried different cycle carriers, I would generally opt for a towbar mounted one, mainly due to the ease of mounting, but also fuel economy.

Roof bars, and also lifting them, are not a solution as the bikes are too heavy

Don't be so sure about that. Mine and my son's machines are MTBs with suspension, mine is a shade under 13Kg and his about 15Kg. His friend has a down hill bike which weighs in at a mighty 22Kg. I use Thule 532 carriers on roof bars on my Saab 9-3. Even with a recently seperated shoulder (AC joint dislocation - a permanent injury) I can lift the bikes on and off quite easily. Use your knees and squat down getting a good grip on the bike before using your legs to do the lifting.
As suggested, remove the battery packs to shed a little weight for carrying. And if two of you can lift the bikes between you, even better.

I used to carry the bikes inside the car with the back seat down and the front wheels removed. If you are thinking of a hatch like the Octavia, then I suggest you seriously consider how lifting these bikes in and out will affect your back as you will have to lean in with them and they are quite heavy at about 25Kg. Provided the car isn't too high, I find the roof solution far superior.

My manager at work goes mountain biking and kite surfing. He carries a lot of kit. His weapon of choice is a Mondeo estate. They are cavernous. There's a lot of cyclists here and with few exceptions the only people who use tow bar mounted carriers are those with 4x4 vehicles. Those who choose to drive cars (which is most of those who aren't eligable for company cars) carry on the roof.