I don't think there is a quick and easy way to turn around a life of
ingrained habits and ways of looking at the world.

The easier and softer the introduction, the less effective and more
recidivist any change will be.

Can I suggest you read Art de Vany's introduction to "evolutionary
fitness" at
http://aris.ss.uci.edu/mbs/personnel/devany/evolutionaryfitness.html

This give you some idea of the magnitude of the change required of them -
and also of the rewards.  Art is older than either of your parents - but
look at the photos!  There is far more to good Paleo health than getting
the food right.  Getting exercise right is probably more important.

In any case, good luck!  In my experience, they'll need a lot of support
and it will probably never end.  If you launch them out in the right
direction, are you in a position to continue the same level of support
when their interest flags, their enthusism wains and their friends tell
them they're nuts?  I do hope so.  The rewards will be great for each of
you.

Keith