Re: Ukemi problems
For rolling, I have found it's best to start total beginners very low, as has been said. Rolling from the knees progressing to rolling standing up but with the hips very low/hands on the ground and so on.
For breakfalls, the best practice seems to be a hip throw along the lines of koshi-nage with a high grade throwing as the beginners tend to thrash about a bit (or freeze). Lots of time to push them into the right shape as they drop.
There's a beauty in rolling that everyone can learn. There's always a couple of bits where it hurts.