Charles de Gaulle to Orly?

9 people in a mini-van with luggage? I'd say that would be a challenge with a full sized van!
The best way to get from CDG to ORY is Le Bus Direct.Line 3. It is 23 EUR per person and takes about 70 to 80 minutes. So renting at Orly will cost you over 200 EUR right from the get go. Are you sure they don't have what you want at the HUGE CDG airport with its myriad rental agencies?

Yes it seems very strange to have the hassle of getting yourselves all the way to the opposite side of Paris to another airport to rent a vehicle - of which there will be more at CDG.

And it's true 9 people in a mini-van with luggage is going to be a tight squeeze.

Just rent at CDG and go to Blois from there.

Ha! We have two cars! Yes, 9 people with luggage would be hard. The whole reason I'm going to Orly is to avoid Paris traffic. So I guess the real question is how bad is Paris traffic on a Friday afternoon to drive from CDG to Blois? Normally I would just plow through but since I will be fighting jet lag I want to make the drive as short as possible.

I'm starting to suspect the longer drive might be better then trying to get to Orly.

CDG to ORY is about 22 miles.. not sure the hassle of moving between airports really saves you any wear and tear or speeds up your exit from Paris

Hopefully you can make the change and not get hit with a rate increase

I might be affected from living in Chicago. I work downtown and take a train home which takes an hour. Driving home on a Friday could take 2-3 hours. Sitting in stop and go traffic while fighting jet lag is what made me think to drive from Orly since we are heading southwest of Paris and CDG is northwest of Paris.
We rented through AutoEurope so I will give them a call and see what they can do.

IMHO, you were on the right track thinking of avoiding Friday afternoon traffic around and out of the Paris region; it's just as bad or worse than Chicago. But what concerns me is this:

since I will be fighting jet lag

You are endangering not only yourself and your passengers, but the others on the road. Couldn't you make alternative plans and take off refreshed on Saturday morning.

You will be IN Paris traffic going from CDG to Orly. The peripherique (ring road) is the worst part of Paris traffic, and you would be needlessly subjecting yourself to more of it with this plan. This is just not a good idea.

Also, as Bets mentioned, not a good idea to drive while jet-lagged.

ks,

For travel between CDG and ORY, I'd use the RER "B" as the two airports are at opposite ends of the line. Travel as far as Antony station and then transfer to the automated Orlyval train. The trip should take about 1H:15M. You could also use the Bus, but of course with that option you'll be subject to traffic delays.

Herding 9 people and their luggage on the train is going to be a nightmare and add over 100 Euro to the cost of the day. Taking the bus from CDG to Orly adds both high cost and subjects you to the traffic. I would rent the cars at CDG and drive around Paris on the ring road if you are coming from another European destination. If you are coming from the US then driving to Blois on arrival is an invitation to killing some innocent person on the road as well as yourselves. Just a really bad idea. You shouldn't have any trouble moving your pick up from Orly to CDG. Adding that hassle of transport is just nuts. Yes the peripherique has a lot of traffic but mid day -- say you get on the road at about 11:30 is not likely to be terrible.