Minecraft Windows 10 Edition False Duplicate Pack

They are incompatible. I had to look this up myself when my children wanted to all play on windows, Xbox and PE. The PE version is fundamentally a different version from the rest of them. Sorry.

No, it is not possible to have different custom skins in separate slots. The easiest thing for you to do would be to keep the skins you want in a special folder so they are easy to find when you need them.

Bedrock Edition has limitations on engine capacity, and therefore cannot store multiple different skins for you, outside of created characters or purchased skins.

You could apply to be a community creator, and, if accepted, release your sets of skins for use by the community, and then save those in separate slots, but that is a complex process that isnt guaranteed to work.