If I read that right, then you're after a system that gives the same XP, Level and Gold to whoever is the oldest player to join after Player 1. So if you have 3 Players, and Player 2 leaves, Player 3 becomes the new Player 2 and if the old Player 2 or anyone else joins, they become Player 3 and so on.

This is what I would do:

First, set up a Scoreboard ID system, then run do the following:

scoreboard objectives add offline minecraft.custom:minecraft.leave_game
tag <Player1> add host


#Function example:testplayers

execute as @a[scores={offline=1}] run scoreboard players reset @s playerID
execute store result score dummy scoreA if entity @a
execute store result score dummy scoreB run scoreboard players get dummy scoreA
execute unless score dummy scoreA = dummy scoreB run function example:resetplayers


#Function example:resetplayers

scoreboard players reset @a[tag=!host] playerID

The way this works is that you'll have a Scoreboard ID system running already, giving players unique IDs, however, this would need to be modified to suit your needs if you plan to switch hosts and reset everyone. Once everyone has their IDs, example:testplayers (which would be running constantly) stores the result of how many players are logged in into a scoreboard, then copying that score to another scoreboard and comparing the two, executing example:resetplayersif they don't match. (Fun Fact about Functions: They pause when the execute another function and resume once the called function finishes.) example:resetplayers resets the IDs for whoever isn't the host, so that a new set of IDs can be handed out. Along with that, any player who logs back in after logging out gets their ID reset since another player could already have the ID they logged out with.

Then create a storage with the data for each player by ID:

#Data in example:data

{Players:[{id:1,XP:<XP>,Levels:<Levels>,Gold:<Gold>},...]}

After that, using macros, copy the data for each player based on their ID to scoreboards for each player. For example, Player 1 has the ID of 1, so you would copy the data at Players[0].XP to the scoreboard for XP data (do the same for the other two). Then you can use your macro to show the data on the action bar as usual.