Wanting to use Ripple to transfer funds with family

[Gilgamesh]

I just created a Rippex wallet for myself and trying to work out how my Dad and I can use Ripple so he can cheaply buy GBP from me using XRP.

So the steps I think we have to go through are:

1. Dad buys XRP from a Japanese exchange and funds his wallet with XRP.

2. He creates a trust line to me for 1000 GBP (as an example).

3. We then agree on a rate (let's say 100 XRP per GBP) and so I create an offer of 1000 GBP.<my wallet address> for 100000 XRP.

4. My dad buys the GBP IOU and I get the XRP.

The part I'm not sure about is how does he redeem the IOU after I give him the physical 1000 GBP?

P.S. I know we can do this transaction without issuing an IOU, but I'd like to understand how it works. Also its means other family members who live in other parts of the world can join in and trade the IOUs between each other. 

Edited June 13, 2017 by Gilgamesh