Example...

I have 3 creatures of the house I have called.

I reap all 3.

Then I play a card that says ready a creature.

Can I reap with that creature for a second time?

Yes

Thank you, that will come in very handy!!

To go even further. Let's stick to your example and let's say your opponent has zero creatures in play. You could reap with all 3 of your creatures, play a card that allows you to "ready and fight" with your creatures and reap with all 3 of them again. Because you ready your creatures, but don't have a target for your creatures, so the rest of the action card fizzles and you are free to do what you want with your now ready creatures