Answer is
1. G, who is a good footballer, had a dad who used to play for Arsenal.
2. The concert, where everyone was dancing, was wonderful.
3. The jacket that you wanted has been sold.
4. They're closing the market where I used to go every week.
5. Daniel, whose mother is the head teacher at my school, is my best friend.
6. Oscar, who has always loved cycling, has a new bike.