It has been my experience that you CAN check in the whole family (even if DH is returning the car). IF you have a valid photo ID for him (like his passport), you can even get his KTTW card. If you do not have a valid photo ID for him, the CM will do the check in but will hold his KTTW card. Then when he gets to the port, he needs to get into that CM's line and he/she will just look at his ID and give him the KTTW card. They do ask that the whole family be together for the security photo, but they make exceptions for people arriving at a different time. You'll probably find it just as easy to wait for dad before doing the security photo.
They SAY that all adults need to be present to check in, but that's not normally enforced as long as you have all the documentation.
If the group is separating, BE SURE the driver keeps one photo ID (like driver's license) with him in order to re-enter the terminal area. Logically, if he's driving to return the car, he needs this anyhow!