Taxis are always total except in Paris if there are more than 4 passengers there is an additional 4 Euro charge for the 5th 6th 7th passenger. So for the 4 of you it would be 58 Euro which should show on the meter (do not let them run the meter). Tips not required -- 60 is reasonable. It would cost you about 42 Euro to take the train, haul luggage up and down stairs, walk and find hotel etc. Taxi absolutely. And do not be deflected by those offering taxi rides (scammers) or directing you to other lines than the official queue which is well signed at the airport. Get in the queue and take your turn.
Don't know when you are coming but FWIW the RER B is not running today and so a complicated route via RER D and shuttle buses is required -- you absolutely don't want to do that.