This is going to sound silly, but ... is Irene sure there isn't a way into her attic space from inside the house? It may be that she has never used it, and never looked for it. If I was going into such a space, I'd rather do it going up from inside if possible.

I don't think mom cat would share a space with racoons since they would regard the kittens as convenient food. So would rats. I think it's amazing that an abandoned cat has managed to secure such a space for her kittens and, even if her kittens can't be saved, I hope she can be helped.

The problem with anyone going in through the hole would be that unless they were completely successful, the mother cat would try to move the kittens again.

Terrible situation but I'm really glad you are doing all you can to help.