Here is what you do, if it is family tell them to give you the receipts.hopefully they can, especially if they know in advance.
Disney policy is you can return gift cards if you have the origin receipts.
Then either in a store or at wdw, return the gifts cards and take the money.
Then and only after you get your money back, buy the gift car with the amount you want on it.
Believe me I have done this, Disney does not like it but it is there policy that you can return gift cards with the original reciept for cash. I have also told everyone to pay cash for then just so no one can say has to go on original credit card, although they have not said that to me at all.
We have been doing this for almost 20 years, my kids have way to much and hate, hate, hate grandmas cloths as gifts. So we do gift cards, aunts, uncles. And everyone started to get in on it, we give to their kids, they give to our kids. At first the kids hated all presents were now gone within family groups. But after a year a and then realizing that they can buy anything they want at Disney they are so happy. Even now in there twenties the kids love when they pool all those gift cards together and get one card for several hundred dollars.
This is the only way I have been able to figure out a way around the consolidating the cards. And yes believe me, Disney hates it. So make sure you do all of them and do not tell them you are going to turn around and buy one card. Don't do one kid at a time and then buy the card because then they will get all hottie on you when you do the next child's.
We turn them all in, if they get hottie just say this is our last day and we did not spend then all and would like to change them for cash. Whatever, it is there policy that it can be done so who cares if they don't like it.what I do then is walk away, sometimes even to a different store or cashier and let the kids pick a card and seperate the money for each child and put it on the new card.
Good luck, if you find an easier way i would like to know, after 20 years this is the only way we have been able to figure it out and it is a pain if it is all small $25 and you have to join 20 of them.
Hope that helps.