We just did this in September and we just checked out in the morning at about 8:00 am, had Hojos call us a cab and it cost about $12.00 with a nice tip.
We then checked in and she gave us our keys and a number to call later. She told me that we would be provided our room # when we called and we wouldn't even need to go to the front desk.
We then checked our luggage with the bell captain which is right near check-in.
We did call later from a phone booth in the parks as our cell phones did not work there, got our room number, returned to the hotel and went straight to our room and called the bell captain to get our bags.
Since there are so many of you, it might be easier to have one of you, maybe you, take the cab with all the luggage and take advantage of the bell captain who will help you with your bags and do all the check-in while your mother, grandma and children have breakfast or something.
One thing that I wanted to mention is that apparently California Adventure does not keep all of their lights on at night all the time.
When we were there in September, the park shut down at 6:00 pm. We had gone to the pool and came back to see all the pretty lights on at about 8:00.
I admired them, went to get the camera and then they all went out!
It was a real bummer!
Otherwise, we really enjoyed our stay there!