If they are visiting WDW a lot, they probably have their system down and don’t need anything for their trip.
Gift cards are a lame gift, but they are the ones I most appreciate when I have an upcoming trip planned.
Right now, MAYBE 50th anniversary items would be appreciated because that’s more special than a random yearly dated shirt.
If you know them REALLY well, you could make a box of “take on travel” items. Things like disposable ponchos, travel size toiletries, single serve snacks. Travel items that get used up.
Maybe they would appreciate things like travel bags that are Disney themed, but they may have all that stuff. Or maybe if based on the kids getting older, maybe they need something new. For example, my niece got old enough for a phone. She might like battery charger for her phone that is hers to be responsible for, but for the rest of us, that’s old news, we have what we want. She’s also now old enough that owning her own Dopp kit/toiletry bag makes sense.
Good luck with this! Buying gifts is hard!