Carrying 4 touring bikes with a car and 4 persons

You could get a roofbox, put your luggage in that, and then put the bikes in the boot if its the Passat estate.  You might need to take the pedals off, etc. and take tools with you but it would a) be much better for fuel consumption, and b) be more difficult to steal your bikes which means you can stop, park, leave the car as you desire without worrying. 

This is what we do - I pack the bikes in with bedding, jackets, etc. to make sure they don't rattle. 

LIke others I have carried 4 bikes (2 adult + 2 kids and later 3 adults and 1 kids) on a Citroen Xsara Picasso (which is suspect is taller than your car but shorter and narrower).
Check the weight limit for your roof, weigh the bikes, the roof bars and (Thule) bike racks. Mine is rated 90kg. We just about stayed under that.
Prior to buying the roof bars and bike racks I tried a 4 bike rear carrier but it put far too much weight on the rear suspension.

Driving to France with the bikes on the roof was no problem - they slow you down a little and reduce fuel consumption. And make sure you don't forget about them at French motorways tolls, car parks, etc!

Pulling out of a motorway service station and finding ourselves in the middle of a line of TdF service vehicles was an entertainng moment.

I have the Thule roofbar system and you can stick as many bike carriers on the roof bars as you want, so in theory you can put 4 on. The way you would do it is slide 2 close to the centre, top and tailed as mentioned, and then fit the outer 2 as close in as fits. The bars allow the carriers to clamp very close to the end of the bars so the bikes can even stick out over the sides (not sure of the legality or wisdom of this).

With heavier touring bikes, you need to be aware of the maximum load weight for the vehicle and/or the roof rack itself. Your manual will state it, and remember that includes the bars and fittings and is usually about 70kg. So 4 heavy bikes and rack could exceed the load capacity of the roof - think emergency stop, not crushing the car! You don't want to jam on the anchors just to end up admiring your precious steeds glide into the car in front.

If you are planning on using the Tunnel, make sure you book on as an oversized vehicle and join the coaches and RVs.

4 bikes also create a lot of windage, be prepared for noticeable loss in performance and significant increase in fuel consumption. Again the rack will specify a maximum design speed, so you might want, with 4 bikes, to plan for a slower journey than with your naked Passat.

Don't forget carbon frames require a specific holder or frame protector.

Remember to keep your team leader's spare bike on the outside for fast access.

I do same with 2 adults + 2 24" kids bikes. 
Halford Aero bars (actually made by Thule!) Got 2 bike fixing new and 2 off of eBay. 
 

Top and tail the bikes so the handle bars don't clash. 

I've also done 1 adult & 2 kids bikes and a half width roof box this way too.  That does involve putting one of the bike racks outside of the roof bar pillars for 1 of its 3 fixing points.

I bought the cheapest Halfords racks and got 4 onto my roof bars fairly easily. The car is a Toyota Verso, so reasonably wide. Bikes went on in alternate directions, and were a mix of large gravel bike, small road bike and 2 hybrids. The hardest part was lifting the heavy hybrids onto the roof - the Verso is quite tall and I have an iffy shoulder, so I took a tiny step ladder to help with loading.

Putting it all together was a pain, so I've kept it all in one piece since. Fitting it back on the car takes 2 people.

This is the current version: https://www.halfords.com/cycling/bike-racks/roof-mounted-bike-racks/half... so £120 for four, assuming you already have roof bars.

I seldom take 4 bikes now so have switched to a 3 bike Saris Bones rack on the tailgate, but I'm not convinced that 4 on the tailgate is sensible for weight reasons. Bikes on the roof are terrible for fuel consumption but abroad, I'd worry about obscured tail lights and inability to wriggle out of police situations in French...

Hope this helps.