Not sure there are even shuttles and they were always terrible.
Surely two people will not be carrying more suitcases than a taxi can handle. Unless you are carrying work materials or massive gifts for relatives or something like that, figure out how to get by on one no more than 25 inch suitcase and a backpack or similar for carry on each . Learned this the hard way.
A regular taxi should be able to hold two people's luggage, but if you have too much there are van cabs at the airport and you can let the dispatcher know you need one. You might have to step aside with your luggage while one is summoned but there are lots at the airport.
There is a fixed price for up to 4 people from CDG 56 to right bank and 65 to left. No other fees.
When ready to return call the G7 English speaking taxi line two days ahead and book a cab letting them now if you need a large cab. I have done this a couple dozen times and they usually ask about cab size and have always been completely reliable. They show up about 5 minutes before the time you booked. We book 4 hours before our flight and are always there 3 hours before for the check in, emigration and security process.