I would have thought your 24-70 would be a good portrait lens. We had some formal indoor family portraits taken last year, and the professional photographer who did them used a 24-70. The results were outstanding, really first class.
I have the 85, and I don't much like it as an indoor lens. It's an odd length, especially on a crop camera; you need to be quite a long way away from your subject and you might find yourself short of room sometimes. In addition, shooting portraits indoors, in low light, without a flash, doesn't always give great results. My favourite indoor lens is my Tamron 28-75, coupled with a Speedlite. It does a great job.