You want to use the Disney gift card site
https://disneygiftcard.com/ and set up an account. Then you can combine up to $1000 worth of GCs onto just 1 of your GCs. I also buy discounted GCs from Target or Costco etc. and then combine them on the Disney site, so I can payoff our reservation without having to deal with a bunch of GCs. I then will combine GCs to make a few $500 GCs to take with us and use them to payoff our room charges every few days.