Use this website:
https://disneygiftcard.com/
It lets you combine your gift cards onto one. Each card can have a max of $1000 and you can have up to 5 cards in the account. Over the past few months I've purchased approx $3,000 in gift cards from Target with the 5% savings. I was able to put those into the website, transfer onto one primary card (or multiple secondary cards) and pay for my Premier pass, and full resort reservation. Make sure you keep the primary card after paying though because if there is any refund needed, it goes back onto that card. And don't lose it if you have a bunch of money on it!