Use multiple 4D skins in the same world
If you want several 4D skins available at once, do not download each skin as a separate addon. Use Skin Bundle to create one download that contains every model you want in the selector.
Why separate downloads can conflict
Each individual download modifies the Minecraft player so it can display custom geometry. When two different addons try to change the player at the same time, Minecraft Bedrock does not merge their skin lists: the pack higher in the world priority order usually wins.
What Skin Bundle does
A bundle combines several skins into a single .mcaddon. Instead of installing several selectors that compete with each other, the download creates one resource pack, one behavior pack and one unified list inside the Skin Selector.
Build your bundle
Open a skin page and select Add to bundle. Repeat this with every skin you want to combine. When the Skin Bundle sidebar contains the right selection, select Download Bundle to download one .mcaddon prepared with those models.
Enable it in Minecraft
Import the bundle .mcaddon and enable both packs in your world: the Resource Pack and the Behavior Pack. Inside the world, use the Skin Selector to switch between the included models. If you want a different combination later, create and download a new bundle from the website.