Will be vacationing 2 weeks on the island of Fur. Will I be able to purchase adult disposable underwear locally or will I need to bring all this with me?
Have you ever tried washable ones?
this is an example of one of many....
Maybe buy one. See if it works and how well it washes up in the shower and dries.
Also, you can buy some online from a location close or in denmark and have them shipped to where you will stay. Then you can have as many as you need or more and not have to worry and also not have to hunt any down.
Fur is a quite small island with limited shopping options. It has one local supermarket, where you can get your usual groceries, but I don't know if they have what you need and I wouldn't count on it. However in Skive, there nearest larger town, you should be able to find what you need. There is a Matas store (www.matas.dk) where you can find a wide range of hygiene products and a pharmacy (Apotek in Danish) https://www.apoteket.dk/apoteker/skive-svane-apotek/egeris-apotek.