Ok, various options for you;
You say Chelsea Tractor by Audi... i am guessing the mighty Q7?
If so then that vehicle has T tracked roofrails and to but bars on is an easy option, Thule make a direct fit kit for that car (and they also supply Audi!)
If you were to put bars on the roof this would enable you to carry upto 4 adult cycles on the roof, however you may struggle with the childrens cycles on roof mounted carriers, however the better Thule carriers are more versatile for both childrens cycles and weird shaped frames like MTB full sus.
Or you have the option of rear mount, either a metal clamp cycle carrier that effectivly clamps onto the tailgate and is very sturdy if fitted correctly or the traditional strap mount, again very secure and effective however rarely fitted correctly. Both of these will be hampered if you have a rear spoiler. There are various options from Thule, Halfords, Karrite, SarisBones and many others.
With the childrens cycles you can get them onto rear mounts using either a false crossbar or just fitting it at a wacky angle.
All rear mounts limit you to 3 cycles max, and low mounts could mean you legally need a lighting board or second rear numberplate.
Another option is a towbar mount, which does exactly that, clamps securely onto the towbar and usually has a lighting board on too, they tilt to allow tailgate access and are very strong and aerodynamic, they also allow any cycle size or frame shape to be carried.
This is my forte, any questions post away or PM me...
And dont buy one without PM'ing me first... i can probably get you the best deal
Keith W "The bus lane warrior!"